travis-ci.yml: only run full check suite from travis cron jobs

.travis.yml

@@ -13,8 +13,7 @@ before_install:
   - cd tests && npm install chalk && cd ..
 
 script:
-  - 'echo "DEBUG: $TRAVIS_BRANCH - $TRAVIS_EVENT_TYPE - $TRAVIS_PULL_REQUEST"'
+  - 'if [[ "$TRAVIS_BRANCH" == "master" && "$TRAVIS_EVENT_TYPE" == "cron" ]]; then make check_all; fi'
-  - 'if [[ "$TRAVIS_BRANCH" == "master" ]]; then make check_all; fi'
   - 'if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then make check_pr; fi'
 
 notifications: