add memory logger to track changes

services/track-changes/app.coffee

@@ -9,6 +9,7 @@ Path = require "path"
 Metrics = require "metrics-sharelatex"
 Metrics.initialize("track-changes")
 Metrics.mongodb.monitor(Path.resolve(__dirname + "/node_modules/mongojs/node_modules/mongodb"), logger)
+Metrics.memory.monitor(logger)
 
 child_process = require "child_process"