Make npm package a bit smaller

[macbre]

Before

$ npm publish --dry-run 2>&1 | egrep 'size|files'

npm notice package size:  392.1 kB                                
npm notice unpacked size: 781.0 kB                                
npm notice total files:   164 

After

npm notice package size:  67.1 kB                                 
npm notice unpacked size: 258.3 kB                                
npm notice total files:   86