Update Sphinx and dependency

Author: brynpickering

changelog.rst

@@ -14,7 +14,7 @@ Release History
 
 |new| `model.backend.rerun()` can work with both `spores` and `plan` run modes (previously only `plan` worked). In the `spores` case, this only works with a built backend that has not been previously run (i.e. `model.run(build_only=True)`), but allows a user to update constraints etc. before running the SPORES method.
 
-|changed||backwards-incompatible| Carrier-specific group constraints are only allowed in isolation (one constraint in the group).
+|changed| |backwards-incompatible| Carrier-specific group constraints are only allowed in isolation (one constraint in the group).
 
 |changed| If `ensure_feasibility` is set to `True`, `unmet_demand` will always be returned in the model results, even if the model is feasible. Fixes issue #355.
 

doc/conf.py

@@ -18,7 +18,7 @@
 sys.path.append(os.path.abspath("_extensions"))
 sys.path.append(os.path.abspath("helpers"))
 
-from sphinx.builders.html import StandaloneHTMLBuilder, SingleFileHTMLBuilder
+from sphinx.builders.singlehtml import StandaloneHTMLBuilder, SingleFileHTMLBuilder
 
 import generate_tables  # from helpers
 

requirements_docs.yml

@@ -5,7 +5,7 @@ channels:
 
 dependencies:
     - python=3.7  # https://docs.readthedocs.io/en/stable/config-file/v2.html#python-version
-    - sphinx>=2.3
+    - sphinx=4.1.2
     - numpydoc
     - ruamel.yaml
     - nbconvert  # To generate HTML files from example notebooks