Revert "chore(cluster): set max #cores to 1 for now (we're maxing memory again)"

This reverts commit 3f5221755c.

src/server.js

@@ -8,11 +8,9 @@ var logging = require('./logging');
 var isProd = nconf.get('NODE_ENV') === 'production';
 var isDev = nconf.get('NODE_ENV') === 'development';
 
-// The max num of CPUs to enable with cluster. On heroku, our app is pretty beefy in memory, so we're knocking back to 1
-var MAX_CORES = 1;
 if (cluster.isMaster && (isDev || isProd)) {
   // Fork workers.
-  _.times(_.min([require('os').cpus().length,MAX_CORES]), function(){
+  _.times(_.min([require('os').cpus().length,2]), function(){
     cluster.fork();
   });