Add ZFS check on macOS

Apparently you can get ZFS on macOS:
https://github.com/openzfsonosx/zfs

Addresses #1, #12, #13

Author: jakewilliami

src/HiddenFiles.jl

@@ -119,7 +119,7 @@ export ishidden
 
 
         #=== All macOS cases ===#
-        _ishidden(f::AbstractString) = _ishidden_bsd_related(f) || _exists_inside_package_or_bundle(f)
+        _ishidden(f::AbstractString) = _ishidden_bsd_related(f) || _exists_inside_package_or_bundle(f) || (iszfs() && _ishidden_zfs(f))
     elseif Sys.isbsd()  # BSD
         _hidden(f::AbstractString) = _ishidden_bsd_related(f) || (iszfs() && _ishidden_zfs(f))
     else  # General UNIX