Update myst-parser requirement from ~=0.13.7 to >=0.13.7,<0.15.0

Updates the requirements on [myst-parser](https://github.com/executablebooks/MyST-Parser) to permit the latest version.
- [Release notes](https://github.com/executablebooks/MyST-Parser/releases)
- [Changelog](https://github.com/executablebooks/MyST-Parser/blob/master/CHANGELOG.md)
- [Commits](executablebooks/MyST-Parser@v0.13.7...v0.14.0)

Signed-off-by: dependabot[bot] <support@github.com>

setup.cfg

@@ -65,7 +65,7 @@ demo =
     ipython
 doc =
     sphinx
-    myst-parser~=0.13.7
+    myst-parser>=0.13.7,<0.15.0
     alabaster
     sphinxcontrib-napoleon
     nbsphinx