Add Travis CI integration (#23)

Run both in 3.6 and 3.7 so that the code is ready for an update.

Author: jdevera

.travis.yml

@@ -0,0 +1,10 @@
+dist: bionic
+language: python
+python:
+    - 3.6
+    - 3.7
+install:
+    - pip install pipenv
+    - pipenv install -d
+script:
+    - pytest