gradle build not working for appengine-java8/endpoints-v2-backend

[mpoehler]

gradle build appengine-java8/endpoints-v2-backend does not work.

During the build the task replaceProjectId replaces the projectId in the wrong file. Is currently exploded-backend, but must be exploded-endpoints-v2-backend.

I'll provide a pull-request in a minute.

[mpoehler]

Fixed with pull request #748