Discord Oauth2 support (#4476)

* add discord auth

* add vendor for discord

* fix syntax error

* make fmt

* update version of goth in use

* update markbates/goth

vendor/github.com/markbates/goth/gothic/gothic.go

@@ -3,7 +3,7 @@ Package gothic wraps common behaviour when using Goth. This makes it quick, and
 and running with Goth. Of course, if you want complete control over how things flow, in regards
 to the authentication process, feel free and use Goth directly.
 
-See https://github.com/markbates/goth/examples/main.go to see this in action.
+See https://github.com/markbates/goth/blob/master/examples/main.go to see this in action.
 */
 package gothic