removed ref to old file name from travis install command

removed deprecated --use-mirrors option from travis install command

.travis.yml

@@ -5,8 +5,8 @@ python:
   - "pypy"
 # command to install dependencies
 install:
-  - pip install . --use-mirrors
-  - pip install -r test_requirements.txt --use-mirrors
+  - pip install .
+  - pip install -r dev_requirements.txt
 # command to run tests
 script: nosetests
 # only notify when status changes from success to failure