keep .highlight css class

highlight area now gets two classes: 'div.highlight.hl-language'

CSS header is generated for class '.highlight',
but cells were given class '.hl-language',
so the CSS wasn't applying correctly.

IPython/nbconvert/filters/highlight.py

@@ -2,41 +2,23 b''
 Module containing filter functions that allow code to be highlighted
 from within Jinja templates.
 """
-#-----------------------------------------------------------------------------
-# Copyright (c) the IPython Development Team.
-#
-# Distributed under the terms of the Modified BSD License.
-#
-# The full license is in the file COPYING.txt, distributed with this software.
-#-----------------------------------------------------------------------------
 
-#-----------------------------------------------------------------------------
-# Imports
-#-----------------------------------------------------------------------------
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
 
 # pygments must not be imported at the module level
 # because errors should be raised at runtime if it's actually needed,
 # not import time, when it may not be needed.
 
-# Our own imports
 from IPython.nbconvert.utils.base import NbConvertBase
 
-#-----------------------------------------------------------------------------
-# Globals and constants
-#-----------------------------------------------------------------------------
-
 MULTILINE_OUTPUTS = ['text', 'html', 'svg', 'latex', 'javascript', 'json']
 
-#-----------------------------------------------------------------------------
-# Utility functions
-#-----------------------------------------------------------------------------
-
 __all__ = [
     'Highlight2HTML',
     'Highlight2Latex'
 ]
 
-
 class Highlight2HTML(NbConvertBase):
 
     def __call__(self, source, language=None, metadata=None):
@@ -58,7 +40,7 b' class Highlight2HTML(NbConvertBase):'
 
         return _pygments_highlight(source if len(source) > 0 else ' ',
                                    # needed to help post processors:
-                                   HtmlFormatter(cssclass="hl-"+language), 
+                                   HtmlFormatter(cssclass=" highlight hl-"+language),
                                    language, metadata)