Normalize GitHub urls

fixes #7

builds on top of #78

ran this though all registered packages and it covers all of them except the following

```JSON
{
    name: 'ember-build-validations',
    url: 'git://github.com/dockyard/ember-builds/tree/master/validations'
},{
    name: 'grid-generator#1.0.1',
    url: 'git://github.com/martinmaricak/Grid-Generator/releases/tag/1.0.1'
},{
    name: 'kojs',
    url: 'git://github.com/SteveSanderson/knockout/blob/master/build/output/knockout-latest.js'
},{
    name: 'linq',
    url: 'git://github.com/mihaifm/linq/blob/master/linq.js'
},{
    name: 'RangeSlider',
    url: 'git://ghusse.github.com/jQRangeSlider'
},{
    name: 'squeezr',
    url: 'git://github.com/jkphl/squeezr/tree/master/squeezr'
}
```

All of which are invalid and can't be downloaded anyway.