Update dependent packages to clear safety errors (#126)

* Prevent updater threads from crashing when access is denied by SCP, as described in #123

* Fix flake8 complaints re whitespace & comments.

* Remove errant ] somehow added to vars in f strings in two log messages.

* Updating urllib3, pylint, pyyaml (and astroid due to dependency) to resolve vulnerabilities reported by safety.:
+==============================================================================+
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|           /$$$$$$$  /$$$$$$ | $$  \__//$$$$$$  /$$$$$$   /$$   /$$           |
|          /$$_____/ |____  $$| $$$$   /$$__  $$|_  $$_/  | $$  | $$           |
|         |  $$$$$$   /$$$$$$$| $$_/  | $$$$$$$$  | $$    | $$  | $$           |
|          \____  $$ /$$__  $$| $$    | $$_____/  | $$ /$$| $$  | $$           |
|          /$$$$$$$/|  $$$$$$$| $$    |  $$$$$$$  |  $$$$/|  $$$$$$$           |
|         |_______/  \_______/|__/     \_______/   \___/   \____  $$           |
|                                                          /$$  | $$           |
|                                                         |  $$$$$$/           |
|  by pyup.io                                              \______/            |
|                                                                              |
+==============================================================================+
| REPORT                                                                       |
| checked 64 packages, using default DB                                        |
+============================+===========+==========================+==========+
| package                    | installed | affected                 | ID       |
+============================+===========+==========================+==========+
| pylint                     | 2.4.2     | <2.5.0                   | 38224    |
+==============================================================================+
| Pylint 2.5.0 no longer allows ``python -m pylint ...`` to import user code.  |
| Previously, it added the current working directory as the first element of   |
| ``sys.path``. This opened up a potential security hole where ``pylint``      |
| would import user level code as long as that code resided in modules having  |
| the same name as stdlib or pylint's own modules.                             |
+==============================================================================+
| pyyaml                     | 5.1.2     | <5.3.1                   | 38100    |
+==============================================================================+
| A vulnerability was discovered in the PyYAML library in versions before      |
| 5.3.1, where it is susceptible to arbitrary code execution when it processes |
| untrusted YAML files through the full_load method or with the FullLoader     |
| loader. Applications that use the library to process untrusted input may be  |
| vulnerable to this flaw. An attacker could use this flaw to execute          |
| arbitrary code on the system by abusing the python/object/new constructor.   |
| See: CVE-2020-1747.                                                          |
+==============================================================================+
| pyyaml                     | 5.1.2     | >=5.1,<=5.1.2            | 38639    |
+==============================================================================+
| CVE-2019-20477: PyYAML 5.1 through 5.1.2 has insufficient restrictions on    |
| the load and load_all functions because of a class deserialization issue,    |
| e.g., Popen is a class in the subprocess module. NOTE: this issue exists     |
| because of an incomplete fix for CVE-2017-18342.                             |
+==============================================================================+
| urllib3                    | 1.25.6    | <1.25.9                  | 38834    |
+==============================================================================+
| urllib3 before 1.25.9 allows CRLF injection if the attacker controls the     |
| HTTP request method, as demonstrated by inserting CR and LF control          |
| characters in the first argument of putrequest(). See: CVE-2020-26137.       |
| (NOTE: this is similar to CVE-2020-26116.)                                   |
+==============================================================================+
| urllib3                    | 1.25.6    | >=1.25.2,<=1.25.7        | 27519    |
+==============================================================================+
| The _encode_invalid_chars function in util/url.py in the urllib3 library     |
| 1.25.2 through 1.25.7 for Python allows a denial of service (CPU             |
| consumption) because of an inefficient algorithm. The percent_encodings      |
| array contains all matches of percent encodings. It is not deduplicated. For |
| a URL of length N, the size of percent_encodings may be up to O(N). The next |
| step (normalize existing percent-encoded bytes) also takes up to O(N) for    |
| each step, so the total time is O(N^2). If percent_encodings were            |
| deduplicated, the time to compute _encode_invalid_chars would be O(kN),      |
| where k is at most 484 ((10+6*2)^2). See: CVE-2020-7212.                     |
+==============================================================================+

requirements.txt

@@ -1,5 +1,5 @@
 aniso8601==8.0.0
-astroid==2.3.1
+astroid==2.4.2
 attrs==19.3.0
 better-exceptions==0.1.7
 blinker==1.4
@@ -43,11 +43,11 @@ more-itertools==7.2.0
 pexpect==4.7.0
 psycopg2==2.7.7
 ptyprocess==0.6.0
-pylint==2.4.2
+pylint==2.6.0
 pyrsistent==0.15.4
 python-dateutil==2.8.0
 pytz==2017.2
-PyYAML==5.1.2
+PyYAML==5.3.1
 requests==2.22.0
 retrying==1.3.3
 s3transfer==0.2.1
@@ -58,7 +58,7 @@ swag-client==0.4.6
 tabulate==0.8.5
 tqdm==4.11.2
 typed-ast==1.4.0
-urllib3==1.25.6
+urllib3==1.26.2
 Werkzeug==0.16.0
 wrapt==1.11.2
 zipp==0.6.0