Run angularjs-update on install

As stated, this pull request runs the angularjs-update script on plugin install. I need this for the CI/CD environment I'm in. The code is checked out in a clean environment every time and I don't have the opportunity to influence the script, the deployment runs "grails compile; grails war".

This change seems to make sense anyway. Checking out fresh and running "compile" or "run-app" will do as expected.