Fixed npm warning about "repositories" property

After adding *svg.js* as a dependency

```
$ npm install svg.js --save                                                                                                                        
svg.js@1.0.1 node_modules/svg.js
```

when I update deps I get a warning

```
$ npm install
npm WARN package.json svg.js@1.0.1 'repositories' (plural) Not supported.
npm WARN package.json Please pick one as the 'repository' field
svg.js@1.0.1 node_modules/svg.js
```