update superagent

the latest superchanged changed the meaning of 'error'. Previously,
error implied a network error. With the latest superagent, error means
a REST api error i.e 4xx, 5xx are flagged as errors.

error && !error.response means network error

src/oauthproxy.js

@@ -92,7 +92,7 @@ function authenticate(req, res, next) {
             .post(config.internalAdminOrigin() + '/api/v1/oauth/token')
             .query(query).send(data)
             .end(function (error, result) {
-            if (error) {
+            if (error && !error.response) {
                 console.error(error);
                 return res.send(500, 'Unable to contact the oauth server.');
             }