mini migrator for spaces in pins

[CJ-Wright]

It would be nice to have a mini migrator that fixes the pin spacing lint

[CJ-Wright]

This is the code doing the linting
https://github.com/conda-forge/conda-smithy/blob/master/conda_smithy/lint_recipe.py#L406

See the pip minimigrator (https://github.com/regro/cf-scripts/blob/master/conda_forge_tick/migrators.xsh#L78) for an example of replacement based migrations.