add changelog

Author: unglaublicherdude

Readme.txt

@@ -56,6 +56,10 @@ While the released code is hosted on the WordPress svn, we develop the plugin on
 
 == Changelog ==
 
+= 3.1.2 =
+
+* checkin composer.lock to actually serve updates
+
 = 3.0.3 =
 
 * Add platform directive (8.1), so we can actually support older php versions.