unused variable groupY and containerWidth

uglify-js is giving me these error messages. 
the minified version is not updated.
Merge pull request #18 from jonathanong/patch-1

unused variable groupY and containerWidth
unused: true in .jshintrc; tick version
Merge branch 'master' of github.com:desandro/vanilla-masonry
Merge remote-tracking branch 'upstream/master'