Removed travis use of no longer supported pip switch --use-mirrors .

Author: amotzg

.travis.yml

@@ -6,7 +6,7 @@ python:
 - '3.4'
 - pypy
 - pypy3
-install: pip install . --use-mirrors
+install: pip install .
 script: python setup.py nosetests
 deploy:
   provider: pypi