common: Updated changelog

common/debian/changelog

+symbiosis-common (2015:1218) stable; urgency=medium
+
+  * The current certificate is now marked for replacement if it is deemed
+    invalid by OpenSSL.
+
+ -- Patrick J Cherry <patrick@bytemark.co.uk>  Wed, 25 May 2016 15:45:59 +0100
+
 symbiosis-common (2015:1217) stable; urgency=medium
 
   * Added --list and --select options for symbiosis-ssl