Update stable tag to version 3.1.2

Author: ocean90

readme.txt

@@ -1,7 +1,7 @@
 === Public Post Preview ===
 Contributors: ocean90
 Tags: public, preview, posts, anonymous, drafts
-Stable tag: 3.1.1
+Stable tag: 3.1.2
 License: GPLv2 or later
 License URI: http://www.gnu.org/licenses/gpl-2.0.html