Specifying conda directive within Snakefile (and even before imports) should be supported

[hermidalc]

With Snakemake you can now specify the conda directive in your Snakefile even before imports to specify global workflow dependencies and environment. https://snakemake.readthedocs.io/en/stable/snakefiles/deployment.html#global-workflow-dependencies

When I define this directive snakefmt thinks it's an error:

InvalidPython: Black error:
Cannot parse: 7:6: conda:

[mbhall88]

This is a duplicate of #209

Global use of conda: was added in v8.0, so will have to wait until we support v8.