brew.sh: handle development git version strings

[EricFromCanada]

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This adds handling of longer git version strings for development builds by splitting the string on dots with read and discarding the fourth dot and anything following. It also accounts for when the build version number is three digits. These example version numbers will now be properly parsed.

This is an alternative to #6319.

Closes #6319

[MikeMcQuaid]

This will just set IFS for this single line, right?

[MikeMcQuaid]

Nice work again @EricFromCanada!