Removed target Python 3.9, as it currently fails (sphinx).

UnsatisfiableError: The following specifications were found to be in conflict:
- python 3.9*
- sphinx -> docutils >=0.11 -> python 3.5* -> libffi >=3.2.1,<3.3a0
- sphinx -> docutils >=0.11 -> python 3.5* -> openssl >=1.0.2n,<1.0.3a
- sphinx -> docutils >=0.11 -> python 3.5* -> readline >=7.0,<8.0a0

.travis.yml

@@ -16,7 +16,6 @@ python:
     - "3.6"
     - "3.7"
     - "3.8"
-    - "3.9"
 
 before_install:
     - bash .travis_dependencies.sh

setup.py

@@ -29,8 +29,7 @@
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
-        "Programming Language :: Python :: 3.8",
-        "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.8"
     ],
     keywords='audio music json',
     license='ISC',