travis test with tox(wip)

Signed-off-by: Hiroshi Miura <miurahr@linux.com>

.travis.yml

@@ -1,5 +1,12 @@
+dist: xenial
+sudo: false
 language: python
-python: 3.6
+matrix:
+  include:
+    - python: 3.7
+      env: TOXENV=check
+    - python: 3.7
+      env: TOXENV=docs
 
 install: pip install tox-travis