Clarify that both files and directories are excluded.

lib/tzinfo/data_sources/zoneinfo_data_source.rb

@@ -78,14 +78,14 @@ class ZoneinfoDataSource < DataSource
       DEFAULT_ALTERNATE_ISO3166_TAB_SEARCH_PATH = ['/usr/share/misc/iso3166.tab', '/usr/share/misc/iso3166'].freeze
       private_constant :DEFAULT_ALTERNATE_ISO3166_TAB_SEARCH_PATH
 
-      # Files in the top level zoneinfo directory that will be excluded from
-      # the list of available time zones:
+      # Files and directories in the top level zoneinfo directory that will be
+      # excluded from the list of available time zones:
       #
       #   - +VERSION is included on Mac OS X.
       #   - leapseconds is a list of leap seconds.
       #   - localtime is the current local timezone (may be a link).
-      #   - posix, posixrules and right are directories containing other versions
-      #     of the zoneinfo files.
+      #   - posix, posixrules and right are directories containing other
+      #     versions of the zoneinfo files.
       #   - SECURITY is included in the Arch Linux tzdata package.
       #   - src is a directory containing the tzdata source included on Solaris.
       #   - timeconfig is a symlink included on Slackware.