Bump version in preparation to release 1.2.0-rc2 (#644)

Bump go build constant version to rc2.

Author: masih

build/openrpc/boost.json.gz

@@ -2,7 +2,7 @@ package build
 
 var CurrentCommit string
 
-const BuildVersion = "1.2.0-rc1"
+const BuildVersion = "1.2.0-rc2"
 
 func UserVersion() string {
 	return BuildVersion + CurrentCommit