diff -uNr pymodbus-2.2.0.old/requirements.txt pymodbus-2.2.0/requirements.txt
--- pymodbus-2.2.0.old/requirements.txt	2019-04-18 10:46:52.000000000 +0200
+++ pymodbus-2.2.0/requirements.txt	2019-06-23 11:00:32.727902663 +0200
@@ -1,4 +1,4 @@
-six==1.11.0
+six>=1.11.0
 # -------------------------------------------------------------------
 # if want to use the pymodbus serial stack, uncomment these
 # -------------------------------------------------------------------