adding mustache mimetype

execute.py

@@ -11,7 +11,7 @@ from nbconvert_fix import ExtractOutputPreprocessor
 
 reader = notedown.MarkdownReader(code_regex='fenced')
 
-mimetypes.add_type('application/vnd.plotly.v1+json', '.json')
+mimetypes.add_type('application/vnd.plotly.v1+json', '.json', '.mustache')
 
 src = Path('src')
 target = Path('docs')