MINOR: lua: add uuid to the Class Proxy

the proxy UUID parameter is not set in the Lua Proxy Class.
This patches adds it.
diff --git a/doc/lua-api/index.rst b/doc/lua-api/index.rst
index 822f8bc..96367f6 100644
--- a/doc/lua-api/index.rst
+++ b/doc/lua-api/index.rst
@@ -823,6 +823,10 @@
 
   Contain the name of the proxy.
 
+.. js:attribute:: Proxy.uuid
+
+  Contain the unique identifier of the proxy.
+
 .. js:attribute:: Proxy.servers
 
   Contain an array with the attached servers. Each server entry is an object of