Add support for Python 3.8

Python 3.8 will thrown an exception if a dict changes while iterating over it,
copy it first.

Fix #890

Author: Jasper Capel

jira/utils/__init__.py

@@ -37,7 +37,7 @@ def __init__(self, *args, **kw):
         super(CaseInsensitiveDict, self).__init__(*args, **kw)
 
         self.itemlist = {}
-        for key, value in super(CaseInsensitiveDict, self).items():
+        for key, value in super(CaseInsensitiveDict, self).copy().items():
             if key != key.lower():
                 self[key.lower()] = value
                 self.pop(key, None)

tox.ini

@@ -5,6 +5,7 @@ requires =
 envlist =
     lint
     pkg
+    py38
     py37
     py36
     py35