Add changelog entry for 3.0.13

Author: XWB

CHANGELOG-3.0.md

@@ -12,6 +12,10 @@ https://github.com/FriendsOfSymfony/FOSElasticaBundle/compare/v3.0.0...v3.0.1
 To generate a changelog summary since the last version, run
 `git log --no-merges --oneline v3.0.0...3.0.x`
 
+* 3.0.13 (2015-xx-xx)
+
+ * Add PHP 7 compatibility
+
 * 3.0.12 (2015-08-31)
 
  * Bump allowed Elastica version to 2.2