Chore: update protobuf & dependencies (#793)

* Chore: update protobuf
* Chore: regenerate mock files
* Chore: update dependencies
* Chore: use Go v1.16.2 and later

app/proxyman/command/command.pb.go

@@ -1,13 +1,12 @@
 // Code generated by protoc-gen-go. DO NOT EDIT.
 // versions:
-// 	protoc-gen-go v1.25.0
-// 	protoc        v3.15.5
+// 	protoc-gen-go v1.26.0
+// 	protoc        v3.15.6
 // source: app/proxyman/command/command.proto
 
 package command
 
 import (
-	proto "github.com/golang/protobuf/proto"
 	v4 "github.com/v2fly/v2ray-core/v4"
 	protocol "github.com/v2fly/v2ray-core/v4/common/protocol"
 	serial "github.com/v2fly/v2ray-core/v4/common/serial"
@@ -24,10 +23,6 @@ const (
 	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
 )
 
-// This is a compile-time assertion that a sufficiently up-to-date version
-// of the legacy proto package is being used.
-const _ = proto.ProtoPackageIsVersion4
-
 type AddUserOperation struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache