build: Fix conda dependency file for documentation build (#1422)

Bumped Python to 3.7
Removed docutils constraint on version 0.12 (resulted in unresolved dependencies)
Added missing dependency myst-parser

Co-authored-by: Johannes Köster <johannes.koester@tu-dortmund.de>

doc-environment.yml

@@ -1,7 +1,7 @@
 channels:
   - conda-forge
 dependencies:
-  - python >=3.5
+  - python >=3.7
   - datrie
   - wrapt
   - pyyaml
@@ -18,6 +18,7 @@ dependencies:
     - sphinxcontrib-napoleon
   - sphinx-argparse
   - sphinx_rtd_theme
-  - docutils==0.12
+  - docutils
   - recommonmark
   - commonmark
+  - myst-parser