Merge remote-tracking branch 'mdboom/use_sphinx_inheritance_diagram'

Author: ddale

doc/conf.py

@@ -25,7 +25,7 @@
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = ['matplotlib.sphinxext.mathmpl', 'math_symbol_table',
               'sphinx.ext.autodoc', 'matplotlib.sphinxext.only_directives',
-              'matplotlib.sphinxext.plot_directive', 'inheritance_diagram',
+              'matplotlib.sphinxext.plot_directive', 'sphinx.ext.inheritance_diagram',
               'gen_gallery', 'gen_rst',
               'matplotlib.sphinxext.ipython_console_highlighting']