[1.11.x] Added release date for 1.11.4.

Backport of 4c68ef9 from master

Author: timgraham

docs/releases/1.11.4.txt

@@ -2,7 +2,7 @@
 Django 1.11.4 release notes
 ===========================
 
-*Under development*
+*August 1, 2017*
 
 Django 1.11.4 fixes several bugs in 1.11.3.