add changelog for 1.2.0

changelog.md

@@ -2,6 +2,18 @@
 
 All notable changes will be documented in this file.
 
+## vNEXT
+
+<a name="1.2.0"></a>
+
+## 1.2.0 (2019-12-24)
+
+- added: ability to change json stringify / json parse methods for DataConnection #592
+
+- removed: `peerBrowser` field from `dataConnection` because unused
+
+- fixed: lastServerId and reconnect #580 #534 #265
+
 <a name="1.1.0"></a>
 
 ## 1.1.0 (2019-09-16)