fix redirect url on login from social

See issue from generator and docs pages: Logging in to social on latest was returning [Object, object] changing one line seems to have fixed it temporarily, but not sure of the implications to the generator.

    // return res.redirect(redirectURL || sessionRedirectURL || '/');
    return res.redirect(sessionRedirectURL || '/');
 
in users.authentication.server.controller at \path\to\project\modules\users\server\controllers\users\users.authentication.server.controller.js

meanjs/generator-meanjs#217

modules/users/server/controllers/users/users.authentication.server.controller.js

@@ -116,7 +116,7 @@ exports.oauthCallback = function (strategy) {
           return res.redirect('/authentication/signin');
         }
 
-        return res.redirect(redirectURL || sessionRedirectURL || '/');
+        return res.redirect(sessionRedirectURL || '/');
       });
     })(req, res, next);
   };