Stop grunt failing on older branches.

It will complain about amd stall file since JS changes in 3.8.

Author: kabalin

.travis.yml

@@ -1,7 +1,7 @@
 language: php
 
 addons:
-  postgresql: "9.4"
+  postgresql: "9.5"
 
 services:
   - mysql
@@ -51,7 +51,7 @@ script:
   - moodle-plugin-ci validate
   - moodle-plugin-ci savepoints
   - moodle-plugin-ci mustache
-  - moodle-plugin-ci grunt
+  - moodle-plugin-ci grunt || [ "$MOODLE_BRANCH" != 'master' -a "$MOODLE_BRANCH" != 'MOODLE_38_STABLE' ]
   - moodle-plugin-ci phpdoc
   - moodle-plugin-ci phpunit --coverage-text
   - moodle-plugin-ci behat --profile $PROFILE