cli/parser: chomp '=' from comma_array flag name

[dawidd6]

brew bump-formula-pr help message:

Before:

        --mirror=                    Use the specified URL as a mirror URL. If
                                     URL is a comma-separated list of URLs,
                                     multiple mirrors will be added.

After:

        --mirror                     Use the specified URL as a mirror URL. If
                                     URL is a comma-separated list of URLs,
                                     multiple mirrors will be added.

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

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[MikeMcQuaid]

What's the advantage of dropping the =?

[dawidd6]

Visual consistency with other flags in the help message. That's it I guess.

[MikeMcQuaid]

Interested in @GauthamGoli and @EricFromCanada's thoughts.

[EricFromCanada]

Unlike a switch which does not take an argument, a flag requires an argument only if defined with a trailing =, which it removes later. The question for comma_array is, since it always requires an argument, should it always be defined with a trailing =, or should it be optional and just removed during parsing? I'd say the latter, which this PR implements, and I'd also say the = should be dropped from bump-formula-pr (requiring a run of brew man).

[GauthamGoli]

Agree with @EricFromCanada.
= is used to differentiate between Optional and Required flag args, comma_array does not need that differentiation.

[MikeMcQuaid]

Thanks again @dawidd6!