Follow middleware naming convention

lib/cartodb/middleware/context/apikey-credentials.js

@@ -1,6 +1,6 @@
 'use strict';
 
-module.exports = function() {
+module.exports = function apikeyToken () {
     return function apikeyTokenMiddleware(req, res, next) {
         const apikeyCredentials = getApikeyCredentialsFromRequest(req);
         res.locals.api_key = apikeyCredentials.token;