Disabled bluebird debug logs

refs TryGhost/Ghost-CLI#778

- enabling the debug logs will eat a huge amount of memory
- ensure we disable the debug logs before we require anything else

core/server/overrides.js

@@ -1,3 +1,10 @@
+/**
+ * If we enable bluebird debug logs we see a huge memory usage.
+ * You can reproduce by removing this line and import a big database export into Ghost.
+ * `NODE_ENV=development node index.js`
+ */
+process.env.BLUEBIRD_DEBUG = 0;
+
 const moment = require('moment-timezone');
 
 /**