Use pipenv for travis ci

Author: kyb3r

.travis.yml

@@ -6,7 +6,7 @@ matrix:
     dist: xenial
 
 install:
-  - pip install -r requirements.txt
-  - pip install pylint
+  - pipenv install
+  - pipenv install pylint
 
-script: python .lint.py
+script: python .lint.py