Removed Javascript from Markdown by adding display priority to def config.

IPython/nbconvert/exporters/markdown.py

@@ -38,6 +38,12 b' class MarkdownExporter(TemplateExporter):'
 
     @property
     def default_config(self):
-        c = Config({'ExtractOutputPreprocessor':{'enabled':True}})
+        c = Config({
+            'NbConvertBase': {
+                'display_data_priority': ['html', 'application/pdf', 'svg', 'latex', 'png', 'jpg', 'jpeg' , 'text']
+            },
+            'ExtractOutputPreprocessor': {
+                'enabled':True}
+            })
         c.merge(super(MarkdownExporter,self).default_config)
         return c