修正代码中的若干拼写错误

cmd/mcping/mcping.go

@@ -1,4 +1,4 @@
-// Useage: go run cmd/ping/ping.go localhost
+// Usage: go run cmd/ping/ping.go localhost
 package main
 
 import (

cmd/substitute_server/substitute.go

@@ -225,8 +225,8 @@ func getStatus() pk.Packet {
 	}
 }
 
-func disconnectID(protocal int32) byte {
-	switch protocal {
+func disconnectID(protocol int32) byte {
+	switch protocol {
 	case 404:
 		return 0x1B
 	case 477, 480:

net/packet/types.go

@@ -13,12 +13,12 @@ type Field interface {
 	FieldDecoder
 }
 
-// A FieldEncoder can be encode as minecraft protocal used.
+// A FieldEncoder can be encode as minecraft protocol used.
 type FieldEncoder interface {
 	Encode() []byte
 }
 
-// A FieldDecoder can Decode from minecraft protocal
+// A FieldDecoder can Decode from minecraft protocol
 type FieldDecoder interface {
 	Decode(r DecodeReader) error
 }