project: Remove matrix build from Travis CI

The tox execution is faster than it takes on Travis CI to spawn new
workers. Also the matrix configuration interferes with the deploy
stage.

.travis.yml

@@ -1,16 +1,8 @@
 language: python
+python:
+  - '2.7'
+  - '3.5'
 install: pip install tox coveralls
-matrix:
-  fast_finish: true
-  include:
-    - python: 3.5
-      env: TOXENV=flake8
-    - python: 3.5
-      env: TOXENV=pylint
-    - python: 2.7
-      env: TOXENV=py27
-    - python: 3.5
-      env: TOXENV=py35
 script: tox
 after_success: coveralls
 deploy: