Fixing Authorization header with basic auth

The http adapater did not remove a custom Authorization header when auth is set.

lib/adapters/http.js

@@ -62,6 +62,10 @@ module.exports = function httpAdapter(config) {
       auth = urlUsername + ':' + urlPassword;
     }
 
+    if (auth) {
+      delete headers.Authorization;
+    }
+
     var isHttps = parsed.protocol === 'https:';
     var agent = isHttps ? config.httpsAgent : config.httpAgent;