[js_highlight.py] Specify except clause with ImportError

Author: jcb91

src/jupyter_contrib_nbextensions/nbconvert_support/js_highlight.py

@@ -21,7 +21,7 @@
 
 try:
     from html.parser import HTMLParser  # py3
-except:
+except ImportError:
     from HTMLParser import HTMLParser  # py2