updates changelog for v0.2.1 (#611)

CHANGELOG.md

+# v0.2.1 - 2020-07-01
+* Adds PoW requirement to faucet payloads
+* Adds tips broadcaster to ensure that all chains are getting solidified
+* Fixes being able to send a double-spend via one node
+* **Breaking**: bumps network and database versions
+
 # v0.2.0 - 2020-06-30
 * Adds the value transfer dApp:
     * New binary transaction layout

plugins/banner/plugin.go

@@ -18,7 +18,7 @@ var (
 
 const (
 	// AppVersion version number
-	AppVersion = "v0.2.0"
+	AppVersion = "v0.2.1"
 
 	// AppName app code name
 	AppName = "GoShimmer"