repoman: remove set literal for python-2.6 compat
diff --git a/bin/repoman b/bin/repoman
index 2f98a9f..2f48934 100755
--- a/bin/repoman
+++ b/bin/repoman
@@ -478,9 +478,9 @@
 	"dev-libs/libusb-compat":"virtual/libusb",
 }
 
-ruby_deprecated = {
+ruby_deprecated = frozenset([
 	"ruby_targets_ree18",
-}
+])
 
 metadata_xml_encoding = 'UTF-8'
 metadata_xml_declaration = '<?xml version="1.0" encoding="%s"?>' % \