Fix Filepath Assumption

This was assuming that you wanted to tack the dest onto the filepath which I think was wrong. Also it doesn't work with the architecture of SNJS module. This just requries you to be more specific when declaring a `src` and `dest`

```javascript
browserifyAliases: {
  directories: [
    {
      src: 'app/assets/js',
      env: ['prod', 'dev', 'test']
    }, {
      src: 'node_modules/snjs/src',
      dest: 'snjs',
      pattern: ['**/*.js', '!**browserify**'],
      env: ['prod', 'dev', 'test']
    }
  ]
}
```