Remove --use-mirrors option to fix the build error of

travis-ci with Python 2.7.12 .

.travis.yml

@@ -3,7 +3,7 @@ sudo: required
 python:
 - '2.7'
 install:
-- pip install -q -e . --use-mirrors
+- pip install -q -e .
 - sudo ./install_dependency.sh
 - sudo rm -rf testkitmerge testkit-merge
 script: