AttributeError: 'str' object has no attribute 'logout'

## Description of the problem
After successfully sent message I'm getting an error:

Cannot invoke service for `fbchat'
Traceback (most recent call last):
File "/opt/mqttwarn/lib/python2.7/site-packages/mqttwarn/core.py", line 508, in processor
notified = timeout(module.plugin, (srv, st))
File "/opt/mqttwarn/lib/python2.7/site-packages/mqttwarn/util.py", line 133, in timeout
raise it.exception
AttributeError: 'str' object has no attribute 'logout'

## Environment information
- Python version: 2.7.18rc1
- `fbchat` version - 1.9.7