Backport PR #10668: Fix #10666: Prepare for removal of sphinx.util.compat module at Sphinx 1.7

Since Sphinx 1.6, the ``sphinx.util.compat.Directive`` class is deprecated. And the entire ``sphinx.util.compat`` module will be removed at 1.7. This PR follows [Sphinx CHANGES](http://www.sphinx-doc.org/en/master/changes.html) tip about using ``docutils.parsers.rst.Directive`` instead.

Relates  10666

IPython/sphinxext/ipython_directive.py

@@ -139,7 +139,7 b' import shutil'
 
 # Third-party
 from docutils.parsers.rst import directives
-from sphinx.util.compat import Directive
+from docutils.parsers.rst import Directive
 
 # Our own
 from traitlets.config import Config