#128: remove usage for pip --use-mirrors in travis ci build

The pip --use-mirrors has been removed and it broke the Travis CI build.

.travis.yml

@@ -5,7 +5,7 @@ python:
   - "2.7"
 
 install: 
-  - "pip install -r requirements.txt --use-mirrors"
+  - "pip install -r requirements.txt"
 
 script: 
   - pybot -P src tests