GRAILS-9834: '<g:external> : media="screen, projector" but should be media="screen, projection"'

new PR for **Grails 2.3.x** branch if this is still relevant

* https://github.com/grails/grails-core/pull/329 (closed)
* https://jira.grails.org/browse/GRAILS-9834

Should I send a PR for 2.4.x branch in addition?