Update S2InitFacebook.groovy

spring security 2 needs 'plugin' not 'plugins' in config file.  Possibly could have both just to keep backwards compatibility?
Merge branch 'patch-1' of github.com:mgkimsal/grails-spring-security-facebook into mgkimsal-patch-1

Conflicts:
	scripts/S2InitFacebook.groovy
Merge branch 'mgkimsal-patch-1' into core2