remove deprecated pip argument

.travis.yml

@@ -17,9 +17,9 @@ env:
 install:
   - "if [[ $TRAVIS_PYTHON_VERSION == '2.7' || $TRAVIS_PYTHON_VERSION == 'pypy' ]]; then pip install configparser; fi"
   - "if [[ $TRAVIS_PYTHON_VERSION != '2.7' && $TRAVIS_PYTHON_VERSION != 'pypy' ]]; then pip install hovercraft; fi"
-  - "pip install -r requirements-test.txt --use-mirrors"
-  - "pip install -q Django==$DJANGO --use-mirrors"
-  - "pip install -e . --use-mirrors"
+  - "pip install -r requirements-test.txt"
+  - "pip install -q Django==$DJANGO"
+  - "pip install -e ."
 
 # command to run tests using coverage, e.g. python setup.py test
 script: coverage run --source waliki runtests.py