support `%matplotlib qt5`

just needed the key, since `%gui qt5` already works

IPython/core/pylabtools.py

@@ -1,24 +1,9 b''
 # -*- coding: utf-8 -*-
-"""Pylab (matplotlib) support utilities.
-
-Authors
--------
-
-* Fernando Perez.
-* Brian Granger
-"""
+"""Pylab (matplotlib) support utilities."""
 from __future__ import print_function
 
-#-----------------------------------------------------------------------------
-#  Copyright (C) 2009  The IPython Development Team
-#
-#  Distributed under the terms of the BSD License.  The full license is in
-#  the file COPYING, distributed as part of this software.
-#-----------------------------------------------------------------------------
-
-#-----------------------------------------------------------------------------
-# Imports
-#-----------------------------------------------------------------------------
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
 
 from io import BytesIO
 
@@ -34,6 +19,7 b" backends = {'tk': 'TkAgg',"
             'wx': 'WXAgg',
             'qt': 'Qt4Agg', # qt3 not supported
             'qt4': 'Qt4Agg',
+            'qt5': 'Qt5Agg',
             'osx': 'MacOSX',
             'inline' : 'module://IPython.kernel.zmq.pylab.backend_inline'}