Allow bower to install with sudo

Without `--allow-root`, bower throws the following:

```
bower ESUDO         Cannot be run with sudo

Additional error details:
Since bower is a user command, there is no need to execute it with superuser permissions.
If you're having permission errors when using bower without sudo, please spend a few minutes learning more about how your system should work and make any necessary repairs.

http://www.joyent.com/blog/installing-node-and-npm
https://gist.github.com/isaacs/579814

You can however run a command with sudo using --allow-root option
```