Fix Gomu's call response (#2251)
Fix Gomu's call response (#2251)

Gomu expects a `map[string]string` type response back, but this isn't
always the case. When Gomu calls a service endpoint that responds with,
let's say, a key where its value is a map or a list, Gomu would be
unable to decode that response. By expecting a `map[string]interface{}`
type response, Gomu is able to decode those responses as well.
myodc/go-micro