fix package.json json format

This commit makes a fis to this error:

```
npm ERR! Failed to parse json
npm ERR! Unexpected token }
npm ERR! File: /home/pvalleri/src/Leaflet.draw.ilvalle/package.json
npm ERR! Failed to parse package.json data.
npm ERR! package.json must be actual JSON, not just JavaScript.
npm ERR! 
npm ERR! This is not a bug in npm.
npm ERR! Tell the package author to fix their package.json file. JSON.parse
```