Forced to manually append the protocol

[mattstyles]

Using node-etcd@beta although I've also been testing on node 5.11.1, I did see that travis is only testing against 4 so not sure if 5 is officially supported, although I dont think its an issue here anyway.

Small one,

const Etcd = require( 'node-etcd' )
const etcd = new Etcd( '10.1.5.1:2379' )

Setting up with just the ip throws an error

[Error: All servers returned error]
  errors: 
   [ { server: '10.1.5.1:2379',
       httperror: [Error: Invalid protocol: 10.1.5.1:],
       httpstatus: undefined,
       httpbody: undefined,
       response: undefined,
       timestamp: Tue May 17 2016 16:02:39 GMT+0000 (UTC) } ],
  retries: 0 }

Manually adding the protocol works just fine.