example cannot work under http protocol

[franklee0817]

I found there's a critical error in transport.Dialer while using transport.HTTP instead of transport.GRPC. The address parameter is like 127.0.0.1:8080. rafthttp.Dialer while pass this address to rafthttp.client thus problems will happen when the leader is trying to communicate with followers. rafthttp.client.Message proceed client request via http.NewRequestWithContext in rafthttp.client.requestProto method. Because the scheme of URL is missing from which we passed (127.0.0.1:8080) in the dialer.

More detail please see net/url.Parse. URL schema is required.

[franklee0817]

bug was found in _examples/raft

[shaj13]

@franklee0817 the caller must start the server for both http and grpc protocols, therefore the caller must set the scheme.
Pass http://127.0.0.1:8080 as address should do the work.
Feel free to re-open