fix typo

converters/transformers.py

@@ -204,7 +204,7 b' class RevealHelpTransformer(ConfigurableTransformers):'
 
     def cell_transform(self, cell, other,count):
         ctype = cell.metadata.get('slideshow',{}).get('slide_type',None)
-        if ctype is None :
+        if ctype in [None, '-'] :
             cell.metadata.slideshow = {}
             cell.metadata.slideshow['slide_type'] = None
         elif ctype == 'fragment':

templates/reveal.tpl

@@ -26,7 +26,7 b''
 <aside class="notes">
 {{ super() }}
 </aside>
-{% elif cell.metadata.slideshow.slide_tyle not in ['skip'] %}
+{% elif cell.metadata.slideshow.slide_type not in ['skip'] %}
 {{ super() }}
 {% endif %}