cli: fix underlined multi-line help text

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Help text such as *May remove files which are shared between applications.* is automatically underlined by CLI::Parser

This pull request fixes underlines for wrapped text made to fit the terminal window.
This can be tested with brew help remove, particularly these two lines:

                                   May remove files which are shared between
                                   applications.

Without this PR, the spaces preceding the word applications are underlined.

[BrewTestBot]

Review period will end on 2020-12-22 at 00:00:00 UTC.

[BrewTestBot]

Review period ended.