Address current CI blocker

[carmocca]

Updating fairscale triggered the following error:

____________________ test_registries_register_automatically ____________________

    def test_registries_register_automatically():
        assert "SaveConfigCallback" not in CALLBACK_REGISTRY
        with mock.patch("sys.argv", ["any.py"]):
>           LightningCLI(BoringModel, run=False, auto_registry=True)

/__w/pytorch-lightning/pytorch-lightning/tests/utilities/test_cli.py:956: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/__w/pytorch-lightning/pytorch-lightning/pytorch_lightning/utilities/cli.py:551: in __init__
    self.setup_parser(run, main_kwargs, subparser_kwargs)
/__w/pytorch-lightning/pytorch-lightning/pytorch_lightning/utilities/cli.py:590: in setup_parser
    self._add_arguments(self.parser)
/__w/pytorch-lightning/pytorch-lightning/pytorch_lightning/utilities/cli.py:630: in _add_arguments
    parser.add_optimizer_args(OPTIMIZER_REGISTRY.classes)
/__w/pytorch-lightning/pytorch-lightning/pytorch_lightning/utilities/cli.py:223: in add_optimizer_args
    self.add_subclass_arguments(optimizer_class, nested_key, **kwargs)
/root/miniconda3/envs/lightning/lib/python3.8/site-packages/jsonargparse/signatures.py:481: in add_subclass_arguments
    doc_group = self._gather_docstrings(baseclass, get_class_init_and_base_docstrings)[0]
/root/miniconda3/envs/lightning/lib/python3.8/site-packages/jsonargparse/signatures.py:527: in _gather_docstrings
    docstring = docstring_parse(doc)
/root/miniconda3/envs/lightning/lib/python3.8/site-packages/docstring_parser/parser.py:42: in parse
    raise exc
/root/miniconda3/envs/lightning/lib/python3.8/site-packages/docstring_parser/parser.py:35: in parse
    ret = module.parse(text)
/root/miniconda3/envs/lightning/lib/python3.8/site-packages/docstring_parser/google.py:295: in parse
    return GoogleParser().parse(text)
/root/miniconda3/envs/lightning/lib/python3.8/site-packages/docstring_parser/google.py:285: in parse
    ret.meta.append(self._build_meta(part, title))
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <docstring_parser.google.GoogleParser object at 0x7fa7b0350220>
text = 'The rest params are in-sync with the `AdaScale` class above.'
title = 'Args'

    def _build_meta(self, text: str, title: str) -> DocstringMeta:
        """Build docstring element.
    
        :param text: docstring element text
        :param title: title of section containing element
        :return:
        """
    
        section = self.sections[title]
    
        if (
            section.type == SectionType.SINGULAR_OR_MULTIPLE
            and not MULTIPLE_PATTERN.match(text)
        ) or section.type == SectionType.SINGULAR:
            return self._build_single_meta(section, text)
    
        if ":" not in text:
>           raise ParseError(f"Expected a colon in {text!r}.")
E           docstring_parser.common.ParseError: Expected a colon in 'The rest params are in-sync with the `AdaScale` class above.'.

There are 3 issues here:

1. https://github.com/facebookresearch/fairscale/blob/e65833a0e4a3d5b0fad6128032746a03a733d275/fairscale/optim/adascale.py#L639 should be unintended.
2. docstring-parse==0.14 started raising this error.
3. jsonargparse should be resilient to these kinds of errors and fallback to something cc @mauvilsa

For now, we can pin docstring-parse==0.13.

cc @tchaton @rohitgr7 @carmocca @akihironitta @Borda