convert couleurs.rb to `depends_on :macos`

from caveats `os_version_only`.
convert deeper.rb to `depends_on :macos`

from caveats `os_version_only`.

Also tweak unrelated version-specific caveat.
convert maintenance.rb to `depends_on :macos`

from caveats `os_version_only`.

Also tweak unrelated version-specific caveat.
convert fenics.rb to `depends_on :macos`

from caveats `os_version_only`.
convert tunnelblick.rb to `depends_on :macos`

from caveats `os_version_only`.
convert ubar.rb to `depends_on :macos`

from caveats `os_version_only`.
convert zooom.rb to `depends_on :macos`

from caveats `os_version_only`.