brew_installer: fix use of force flag

[yelsa]

Fixes passing brew bundle --force to:

• make formula installation run brew install <formula> --force --overwrite
• run brew link --overwrite <formula> to force relinking of an unlinked non-keg by default (i.e. link: nil)

Previously =>

$ brew bundle --force --verbose $ Installing gnupg formula. It is not currently installed.

Now =>

$ brew bundle --force --verbose $ Installing gnupg formula with --force --overwrite. It is not currently installed.