Fix Filepath Assumtion

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']
        }
      ]
    }
```