Implement review feedback

* improve wording on testing with fox (contribute.rst)
* fix whitespace (.travis.xml)

.travis.yml

@@ -9,10 +9,10 @@ env:
   - TOX_ENV=py34
   - TOX_ENV=py35
 matrix:
-    include:
-        - python: 3.6
-          env:
-              - TOX_ENV=py36
+  include:
+    - python: 3.6
+      env:
+      - TOX_ENV=py36
 addons:
   apt_packages:
     - pandoc

docs/contribute.rst

@@ -47,7 +47,7 @@ Or using ``pip``::
 
     $ pip install -e .
 
-To conveniently test vs multiple python versions we also provide a tox file.
+To conveniently test on multiple Python versions, we also provide a .tox file.
 
 
 Building the docs