Create /var/cache/repo-checker for Travis

.travis.yml

@@ -6,6 +6,7 @@ python:
 install:
   - pip install python-coveralls
   - pip install -r requirements.txt
+  - mkdir -p /var/cache/repo-checker
 # command to run tests, e.g. python setup.py test
 script:
   - nosetests --with-coverage --cover-package=oscs,osclib --cover-inclusive