aiomqtt: peg requirement to 1.2.1 or older

Issue: #13
Incompatible with aiomqtt 2.0.0

This is a temporary fix, pending the implementation
of modifications mentioned in:
https://sbtinstruments.github.io/aiomqtt/migration-guide-v2.html

Co-authored-by: Norman Rasmussen <norman@rasmussen.co.za>
Signed-off-by: Flavio Fernandes <flavio@flaviof.com>

requirements.txt

@@ -1,4 +1,4 @@
-aiomqtt
+aiomqtt<=1.2.1
 asyncio-throttle
 paho-mqtt
 python-kasa