Version lock for jupyter-client (#211)

* move to single requirements-dev without lux-widget install manually

* pin jedi version

* pin jupyter-client version

* add back old travis and requirement-dev

.travis.yml

@@ -2,13 +2,13 @@ language: python
 python:
   - "3.7"
 install:
+  - pip install jupyter-client==6.1.6
   - pip install -r requirements.txt
   - pip install -r requirements-dev.txt
-  - pip install git+https://github.com/lux-org/lux-widget
 # command to run tests
 script:
   - black --target-version py37 --line-length 105 --check .
   - python -m pytest tests/*.py
   - pytest --cov-report term --cov=lux tests/
 after_success:
-  - bash <(curl -s https://codecov.io/bash)
+  - bash <(curl -s https://codecov.io/bash)