Set the diff-match-patch timeout to 100ms

This might result in worse diffs, but we don't want to spend a second
blocking the event loop while we figure out nicer diffs when comparing
documents.

services/document-updater/app/js/DiffCodec.js

@@ -1,6 +1,9 @@
 const DMP = require('diff-match-patch')
 const dmp = new DMP()
 
+// Do not attempt to produce a diff for more than 100ms
+dmp.Diff_Timeout = 0.1
+
 module.exports = {
   ADDED: 1,
   REMOVED: -1,