Update ACE to 1.2.6

Fixes input problems with compose key in Chrome 53+ - has been reported
for Chinese and Hangul at least.

Gemfile.lock

@@ -2,7 +2,7 @@ GEM
   remote: https://rubygems.org/
   specs:
     RedCloth (4.3.2)
-    ace-rails-ap (4.1.0)
+    ace-rails-ap (4.1.2)
     actionmailer (4.2.8)
       actionpack (= 4.2.8)
       actionview (= 4.2.8)

changelogs/unreleased/update-ace.yml

+---
+title: Update code editor (ACE) to 1.2.6, to fix input problems with compose key
+merge_request:
+author: