chore(ci): validate commit message when asked, only run tests once

We only validate comment message when `VALIDATE_COMMIT_MSG` is set,
and don't run Travis twice anymore.

Fixes #2766

.travis.yml

@@ -35,7 +35,7 @@ before_script:
   - sh -e /etc/init.d/xvfb start
   - npm run init
   - export $(openssl aes-256-cbc -pass env:CREDENTIALS_PASS -d -in credentials)
-  - 'if [ "$VALIDATE_COMMIT_MSG" == "true" ]; then npm run travis; else ./scripts/validate-commit-msg.sh $TRAVIS_COMMIT; fi'
+  - 'if [ "$VALIDATE_COMMIT_MSG" == "true" ]; then ./scripts/validate-commit-msg.sh $TRAVIS_COMMIT; fi'
   - 'if [ "$LINT" == "true" ]; then npm run lint; fi'
 
 script: