Update dependencies (#975)

vendor/github.com/bwmarrin/discordgo/discord.go

@@ -21,7 +21,7 @@ import (
 )
 
 // VERSION of DiscordGo, follows Semantic Versioning. (http://semver.org/)
-const VERSION = "0.20.1"
+const VERSION = "0.20.2"
 
 // ErrMFA will be risen by New when the user has 2FA.
 var ErrMFA = errors.New("account has 2FA enabled")

vendor/github.com/bwmarrin/discordgo/restapi.go

@@ -88,7 +88,12 @@ func (s *Session) RequestWithLockedBucket(method, urlStr, contentType string, b
 		req.Header.Set("authorization", s.Token)
 	}
 
-	req.Header.Set("Content-Type", contentType)
+	// Discord's API returns a 400 Bad Request is Content-Type is set, but the
+	// request body is empty.
+	if b != nil {
+		req.Header.Set("Content-Type", contentType)
+	}
+
 	// TODO: Make a configurable static variable.
 	req.Header.Set("User-Agent", s.UserAgent)