Support for a proxy by default.

I was using the proxy feature of component (a node app *on a corporate network!*) but since version 1 this feature was removed and hasn't yet been added back.

This is a one-line change to add back support for proxies.

Additionally I notice that Component itself needs to have [line 14 uncommented and line 12 removed](https://github.com/component/component/blob/master/bin/component-install#L14) so that people can specify the proxy manually if they wish.