enforce recommonmark version (#383)

Workaround for bug readthedocs/recommonmark#130

.travis.yml

@@ -8,7 +8,7 @@ before_install:
 - 'if [ "$TRAVIS_PULL_REQUEST" = "false" ]; then openssl aes-256-cbc -K $encrypted_8cdc3d1850ac_key -iv $encrypted_8cdc3d1850ac_iv -in deploy_key.enc -out deploy_key -d; fi'
 install:
 - pip install Sphinx===1.6.6
-- pip install recommonmark
+- pip install recommonmark==0.4.0
 - pip install sphinxcontrib.youtube
 script:
 - ./tests.sh