fix npm3 build updating uglifyjs to version 2

[heldr]

UglifyJS 1 fails on NPM 3 since it needs grunt explicitly defined as dependency.

So, following #69 stats.

UglifyJS 1

$ gzipped dist/clipboard.min.js                  
Original size: 7.67 kB
Compressed size: 2.61 kB
Compression ratio: 33.99%

UglifyJS 2 (with mangle and screw ie8 option)

$ gzipped dist/clipboard.min.js
Original size: 7.70 kB
Compressed size: 2.60 kB
Compression ratio: 33.73%

[zenorocha]

Just started reviewing :)

Sent from GH.

[zenorocha]

Hey @heldr, looks good!

In order to accept this, you need to remove the changes in the minified file. You can just commit the changes on the package.json and push force.

[heldr]

@zenorocha done! 🍵

[zenorocha]

Thanks!