Add Member to MessageReactionAdd (#1042)

https://discord.com/developers/docs/topics/gateway#message-reaction-add

events.go

@@ -194,6 +194,7 @@ func (m *MessageDelete) UnmarshalJSON(b []byte) error {
 // MessageReactionAdd is the data for a MessageReactionAdd event.
 type MessageReactionAdd struct {
 	*MessageReaction
+	Member *Member `json:"member,omitempty"`
 }
 
 // MessageReactionRemove is the data for a MessageReactionRemove event.