use mathjax-style for math passing through pandoc to html

IPython/nbconvert/filters/markdown.py

@@ -52,7 +52,7 b' def markdown2latex(source):'
 
 def markdown2html(source):
     """Convert a markdown string to HTML via pandoc"""
-    return pandoc(source, 'markdown', 'html')
+    return pandoc(source, 'markdown', 'html', extra_args=['--mathjax'])
 
 def markdown2rst(source):
     """Convert a markdown string to LaTeX via pandoc.