Update paho-mqtt to 1.4.0 (#67)

requirements.txt

@@ -1,6 +1,6 @@
 #git+https://github.com/open-homeautomation/miflora.git#egg=miflora
 miflora==0.4
-paho-mqtt==1.3.0
+paho-mqtt==1.4.0
 wheel==0.29.0
 sdnotify==0.3.1
 colorama==0.3.9