Bump version to v0.21.0-devel

discord.go

@@ -21,7 +21,7 @@ import (
 )
 
 // VERSION of DiscordGo, follows Semantic Versioning. (http://semver.org/)
-const VERSION = "0.20.0-alpha"
+const VERSION = "0.21.0-devel"
 
 // ErrMFA will be risen by New when the user has 2FA.
 var ErrMFA = errors.New("account has 2FA enabled")