Update dict.items() for Python 3 compatibility

In Python 3 `items()` return iterators, and a list is never fully
build. The `items()` method in Python 3 works like `viewitems()` in
Python 2.7.

For more information see:
https://docs.python.org/3/whatsnew/3.0.html#views-and-iterators-instead-of-lists

Author: roaldnefs

messagebird/base.py

@@ -2,7 +2,7 @@
 
 class Base(object):
   def load(self, data):
-    for name, value in data.items():
+    for name, value in list(data.items()):
       if hasattr(self, name):
         setattr(self, name, value)