Update changelog for 40.2-1pureos1 release

debian/changelog

+epiphany-browser (40.2-1pureos1) byzantium; urgency=medium
+
+  * Release to byzantium
+  * Add a back button to the Firefox Sync dialog
+
+ -- Alexander Mikhaylenko <alexander.mikhaylenko@puri.sm>  Mon, 02 Aug 2021 15:44:05 +0500
+
 epiphany-browser (40.2-1) experimental; urgency=medium
 
   * New upstream release