Compatibility with Python 3.11.2 #45

Can you make it compatible with Python 3.11.2 ?

It has few errors like:
client.send_message("test")
File "/usr/local/lib/python3.11/dist-packages/pushover.py", line 259, in send_message
for key, value in kwords.iteritems():
^^^^^^^^^^^^^^^^
AttributeError: 'dict' object has no attribute 'iteritems'