gridster/fix: calculating container_width correctly

Thanks @badtant for the notice (https://github.com/ducksboard/gridster.js/commit/3d755fd793e7e74cbdc56d9a86143f4ebf779a98#commitcomment-3423763)
grunt/config: change output file names due to the name change in package.json

Package name was changed from `jquery.gridster` to `gridster`
update dist