Add Pinned to Message struct (#633)

* Bump to v0.17.0

* Add members from GuildMembersChunk to state (#454)

* Revert "Add members from GuildMembersChunk to state (#454)" (#455)

This reverts commit e4487b30d4d846b1fdc08fd3982bd5b9965a8cc9.

* added clarification when initializing discordgo

from the code I ran on my system with the latest changes this seems to be the syntax for the authentication tokens. I'm guessing it was just never updated.
Let me know if this is incorrect. 
Thanks!

* travis: update go versions

* Add Pinned member to message struct

Pinned member was missing.

* Missed an :

* Update README.md

* Removed space

message.go

@@ -80,6 +80,9 @@ type Message struct {
 	// A list of reactions to the message.
 	Reactions []*MessageReactions `json:"reactions"`
 
+	// Whether the message is pinned or not.
+	Pinned bool `json:"pinned"`
+
 	// The type of the message.
 	Type MessageType `json:"type"`