Remove a misspelled copy of EndpointGuildInvites. Issue #440 (#441)

Reference Issue: https://github.com/bwmarrin/discordgo/issues/440
This endpoint was declard twice in endpoints.go, and used in the
GuildInvites() method on Session values. I replaced the misspelled
invocation.

All tests pass.

endpoints.go

@@ -71,7 +71,6 @@ var (
 	EndpointUserNotes          = func(uID string) string { return EndpointUsers + "@me/notes/" + uID }
 
 	EndpointGuild                = func(gID string) string { return EndpointGuilds + gID }
-	EndpointGuildInivtes         = func(gID string) string { return EndpointGuilds + gID + "/invites" }
 	EndpointGuildChannels        = func(gID string) string { return EndpointGuilds + gID + "/channels" }
 	EndpointGuildMembers         = func(gID string) string { return EndpointGuilds + gID + "/members" }
 	EndpointGuildMember          = func(gID, uID string) string { return EndpointGuilds + gID + "/members/" + uID }

restapi.go

@@ -907,7 +907,7 @@ func (s *Session) GuildChannelsReorder(guildID string, channels []*Channel) (err
 // GuildInvites returns an array of Invite structures for the given guild
 // guildID   : The ID of a Guild.
 func (s *Session) GuildInvites(guildID string) (st []*Invite, err error) {
-	body, err := s.RequestWithBucketID("GET", EndpointGuildInvites(guildID), nil, EndpointGuildInivtes(guildID))
+	body, err := s.RequestWithBucketID("GET", EndpointGuildInvites(guildID), nil, EndpointGuildInvites(guildID))
 	if err != nil {
 		return
 	}