(choria-io#267) correctly pass request time to ruby shim

The request time was incorrectly passed to the ruby shim resulting
in null timestamps in logs and failure in anything that needed the
real timestamp

mcorpc/ruby/agent.go

@@ -25,7 +25,7 @@ type ShimRequest struct {
  CallerID string `json:"callerid"`
  Collective string `json:"collective"`
  TTL int `json:"ttl"`
- Time int64 `json:"time"`
+ Time int64 `json:"msgtime"`
  Body *ShimRequestBody `json:"body"`
 }