reinstall dependencies

.travis.yml

 python:
   - "3.4"
 install:
-  - "pip install -r --reinstall tests_requirements.txt"
+  - "pip install -r tests_requirements.txt --upgrade"
   - "pip install python-coveralls"
 script:
   - coverage run tests.py --rcfile=.coveragerc -v && coverage report -m && python3.4 tests.py