Fix gruntfile for builds
Fix gruntfile for builds

This updates the gruntfile to correctly reflect how options should be
passed into the builder: `main` and `config` are part of the `steal`
options object. Also, main is needed so that will be used as the entry
point instead of Grunt's `files`.

tracer99/canjs,gsmeets/canjs,rjgotten/canjs,Psykoral/canjs,patrick-steele-idem/canjs,rasjani/canjs,gsmeets/canjs,gsmeets/canjs,patrick-steele-idem/canjs,rjgotten/canjs,Psykoral/canjs,ackl/canjs,rasjani/canjs,beno/canjs,beno/canjs,tracer99/canjs,bitovi/canjs,rjgotten/canjs,whitecolor/canjs,whitecolor/canjs,bitovi/canjs,ackl/canjs,bitovi/canjs,ackl/canjs,bitovi/canjs,rasjani/canjs,beno/canjs,rjgotten/canjs,whitecolor/canjs,Psykoral/canjs,patrick-steele-idem/canjs,tracer99/canjs,rasjani/canjs,Psykoral/canjs