only verify defs if have commit range

Author: jasonkarns

.travis.yml

@@ -6,5 +6,5 @@ jobs:
   include:
     - stage: test
     - stage: verify definitions
-      if: type = pull_request
+      if: env(TRAVIS_COMMIT_RANGE) is present
       script: npm run verify-definitions -- $TRAVIS_COMMIT_RANGE