discovery: error string lint fixes

discovery: lint fix to remove append loop

discovery/bootstrapper.go

@@ -350,7 +350,7 @@ func (d *DNSSeedBootstrapper) fallBackSRVLookup(soaShim string,
 
 	// If the message response code was not the success code, fail.
 	if resp.Rcode != dns.RcodeSuccess {
-		return nil, fmt.Errorf("Unsuccessful SRV request, "+
+		return nil, fmt.Errorf("unsuccessful SRV request, "+
 			"received: %v", resp.Rcode)
 	}