Remove obsolete pip flag --use-mirrors in travis config

Author: hirunatan

.travis.yml

@@ -3,10 +3,10 @@ python:
   - "2.6"
   - "2.7"
 install:
-  - pip install django --use-mirrors
-  - pip install python-magic --use-mirrors
-  - pip install -e . --use-mirrors
-  - pip install coveralls --use-mirrors
+  - pip install django
+  - pip install python-magic
+  - pip install -e .
+  - pip install coveralls
 script:
   - coverage run --source=validatedfile runtests.py
 notifications: