Adding envvar replacement for groovyFilePath
update parent plugin version to get to compile with java7

Suggestion from here:
https://github.com/jenkinsci/walldisplay-plugin/pull/13
moved envVar replace to just get passed to evaluateGroovyScriptFilePath

not great, but might compile this time...
Merge pull request #4 from bobtheshrew/patch-2

Adding envvar replacement for groovyFilePath