Fill in release date for 1.13.1

CHANGELOG.txt

@@ -29,7 +29,7 @@ Changelog
  * Fix: Fixed incorrect z-index on userbar causing it to appear behind page content (Stein Strindhaug)
 
 
-1.13.1 (xx.xx.20xx) - IN DEVELOPMENT
+1.13.1 (17.11.2017)
 ~~~~~~~~~~~~~~~~~~~
 
  * Fix: API listing views no longer fail when no site records are defined (Karl Hobley)

docs/releases/1.13.1.rst

@@ -1,6 +1,6 @@
-=============================================
-Wagtail 1.13.1 release notes - IN DEVELOPMENT
-=============================================
+============================
+Wagtail 1.13.1 release notes
+============================
 
 .. contents::
     :local: