Update ACE Editor to version 1.2.9

The new ACE editor introduces full support for emojis (and, thereby, UTF-16 characters with high- and low-surrogates). Hence, we can remove our custom fix.

Further, this update will allow emojis to be used in pair programming sessions.

vendor/assets/javascripts/ace/mode-properties.js

@@ -61,6 +61,7 @@ var PropertiesHighlightRules = require("./properties_highlight_rules").Propertie
 
 var Mode = function() {
     this.HighlightRules = PropertiesHighlightRules;
+    this.$behaviour = this.$defaultBehaviour;
 };
 oop.inherits(Mode, TextMode);