Add a magic comment to help go-app-builder find internal.Main.
Add a magic comment to help go-app-builder find internal.Main.

Change-Id: I90fbe66e26fe20c363116a73c1111f306f590a8d

golang/appengine,skyeunknown084/appengine,mzimmerman/appengine,fuchsia-mirror/third_party-github.com-golang-appengine,fuchsia-mirror/third_party-github.com-golang-appengine,mzimmerman/appengine,flowlo/appengine,skyeunknown084/appengine,mzimmerman/appengine,flowlo/appengine,golang/appengine,skyeunknown084/appengine,flowlo/appengine