Added dev req. to travis build

Author: Jan Schaffranek

.travis.yml

@@ -4,7 +4,7 @@ python:
 sudo: false
 # command to install dependencies
 install:
-  - pip install -r requirements.txt
+  - pip install -r requirements-dev.txt
 # command to run tests
 script:
   - make test code-style code-lint