Homebrew: fix `ng` support

This week I decided to try out the `ng` branch of pacapt, but noticed nothing
seemed to work with homebrew:

    [$]> ./compile.sh > pacapt.dev && ./pacapt.dev -Ss foo
    pacapt version 'a411f26' has been generated
    homebrew: 'S:s:' operation is invalid or not implemented.

A little bit of investigation showed it was due to a typo in the name
'homebrew', causing none of the defined functions to match the grep and end up
in `_validate_operation()`'s list.

With this patch, everything operates as expected:

    [$]> ./compile.sh > pacapt.dev && ./pacapt.dev -Ss foo
    pacapt version 'a411f26' has been generated
    No formula found for "foo".
    Searching pull requests...
    Closed pull requests:
    Blacklist foo to prevent terrible bug reports (https://github.com/Homebrew/homebrew/pull/18002)
Merge pull request #32 from xiongchiamiov/homebrew--fix-support-on-ng

Homebrew: fix `ng` support