Fix %env for Python 3. Reviewed in PR #1602.

IPython/core/magic.py

@@ -2943,7 +2943,7 Defaulting color scheme to 'NoColor'"""
     def magic_env(self, parameter_s=''):
         """List environment variables."""
 
-        return os.environ.data
+        return dict(os.environ)
 
     def magic_pushd(self, parameter_s=''):
         """Place the current dir on stack and change directory.