Index: nbconvert-6.3.0/nbconvert/filters/markdown_mistune.py
===================================================================
--- nbconvert-6.3.0.orig/nbconvert/filters/markdown_mistune.py
+++ nbconvert-6.3.0/nbconvert/filters/markdown_mistune.py
@@ -18,7 +18,7 @@ except ImportError:
     # Python 2
     from cgi import escape as html_escape
 
-import mistune
+from nbconvert.vendor import mistune
 
 from pygments import highlight
 from pygments.lexers import get_lexer_by_name
Index: nbconvert-6.3.0/setup.py
===================================================================
--- nbconvert-6.3.0.orig/setup.py
+++ nbconvert-6.3.0/setup.py
@@ -212,7 +212,6 @@ setup_args = dict(
 )
 
 setup_args['install_requires'] = [
-    'mistune>=0.8.1,<2',
     'jinja2>=2.4',
     'pygments>=2.4.1',
     'jupyterlab_pygments',