Typo in package.json

Hi,
I think that `package.json` should be updated from
```
{
   "main": "split-pane.js",
   ...
}
```
to
```
{
  "main": "angular-split-pane.js",
   ...
}
```
otherwise `require` will fail to locate the library:
`require('@shagstrom/angular-split-pane')`
`Cannot find module '@shagstrom/angular-split-pane'`
(tested in Electron 2.0.7)