fix bug with pandas (#697)

i found a bug where you were using a variable "obj" that wasn't defined

twint/output.py

@@ -190,7 +190,7 @@ async def Users(u, config, conn):
 
     if config.Pandas:
         logme.debug(__name__+':User:Pandas+user')
-        panda.update(obj, config)
+        panda.update(user, config)
 
     _output(user, output, config)