Add a travis check that code is black formatted (#43)

.travis.yml

@@ -7,6 +7,8 @@ python:
 install:
   - pip install -r dev_requirements.txt
   - pip install --force-reinstall azure-nspkg==1.0.0
+before_script:
+  - if [[ "$TRAVIS_PYTHON_VERSION" == "3.6" ]]; then black . --line-length 100 --check; fi
 script:
   - pytest azure-kusto-data
   - pytest azure-kusto-ingest

dev_requirements.txt

@@ -1,3 +1,4 @@
 -e azure-kusto-data
 -e azure-kusto-ingest
 pytest>=3.2.0
+black;python_version == '3.6'