TypeError: add_source_parser() positional arguments error in Sphinx v…

…3.0.0

following the recommendation here sphinx-doc/sphinx#7420
changed m2r to m2r @ git+https://github.com/crossnox/m2r@dev#egg=m2r sphinx-doc/sphinx#7479

environment.yml

@@ -4,7 +4,7 @@ channels:
 dependencies:
   - flake8
   - jinja2
-  - m2r
+  - m2r @ git+https://github.com/crossnox/m2r@dev#egg=m2r
   - markdown
   - pyviz::nbsite
   - pyviz::nbsmoke