Add missing RPC command

lib/rpc.js

@@ -25,6 +25,7 @@ const UNAUTHENTICATED_CALLS = {
     IS_CHANNEL_PINNED: Pinning.isChannelPinned,
     IS_NEW_CHANNEL: Channel.isNewChannel,
     WRITE_PRIVATE_MESSAGE: Channel.writePrivateMessage,
+    GET_METADATA: Metadata.getMetadata,
 };
 
 var isUnauthenticateMessage = function (msg) {