Fill in release date for 1.12.2

CHANGELOG.txt

@@ -18,7 +18,7 @@ Changelog
  * Fix: Deletion of image / document files now only happens when database transaction has completed (Gordon Pendleton)
 
 
-1.12.2 (xx.xx.xxxx) - IN DEVELOPMENT
+1.12.2 (18.09.2017)
 ~~~~~~~~~~~~~~~~~~~
 
  * Fix: Migration for addition of `Page.draft_title` field is now reversible (Venelin Stoykov)

docs/releases/1.12.2.rst

@@ -1,6 +1,6 @@
-=============================================
-Wagtail 1.12.2 release notes - IN DEVELOPMENT
-=============================================
+============================
+Wagtail 1.12.2 release notes
+============================
 
 .. contents::
     :local: