fix: callback support on implicit grant type's saveToken model function

Author: adieuadieu

lib/grant-types/implicit-grant-type.js

@@ -7,6 +7,7 @@
 var AbstractGrantType = require('./abstract-grant-type');
 var InvalidArgumentError = require('../errors/invalid-argument-error');
 var Promise = require('bluebird');
+var promisify = require('promisify-any').use(Promise);
 var util = require('util');
 
 /**
@@ -76,7 +77,7 @@ ImplicitGrantType.prototype.saveToken = function(user, client, scope) {
         scope: scope
       };
 
-      return this.model.saveToken(token, client, user);
+      return promisify(this.model.saveToken, 3).call(this.model, token, client, user);
     });
 };