Default `url` typo

[levithomason]

I believe there is a typo in the default url in proxy.js @ ln 58. Should .com//services actually be com/services?

var params = {
-  url: sfEndpoint || "https://login.salesforce.com//services/oauth2/token",
+  url: sfEndpoint || "https://login.salesforce.com/services/oauth2/token",
  method: req.method,
  headers: headers
};