Requires pusher-js if using socket.io

[petecoop]

I'm getting Cannot find module 'pusher-js' when packing with browserify and need to require it even when using socket.io.

Could it be moved to outside in a similar way to socket.io? I'd imagine there would be other connectors in the future, and think it would be best if you just install the library for the connector you are using.

[petecoop]

As a quick workaround for this I'm using .ignore('pusher-js) in my browserify setup in gulp which just replaces it with an empty object. But would be nice to not have to do this