Attempt to fix Travis-CI build issues with newer version of keyring

According to this advice:
https://github.com/jaraco/keyring/issues/203#issuecomment-176296396

.travis.yml

@@ -12,6 +12,7 @@ matrix:
 install:
   - pip install -r requirements.txt
   - pip install -r requirements-dev.txt
+  - pip install -r requirements-travis.txt
   - pip install coveralls
 # command to run tests
 script: py.test coursera/test -v --cov coursera --cov-report html

requirements-travis.txt

@@ -0,0 +1 @@
+keyrings.alt