update usages of singleton

extra/db/types/types.factor

@@ -4,7 +4,7 @@ USING: arrays assocs db kernel math math.parser
 sequences continuations sequences.deep sequences.lib
 words namespaces tools.walker slots slots.private classes
 mirrors classes.tuple combinators calendar.format symbols
-singleton ;
+classes.singleton ;
 IN: db.types
 
 HOOK: modifier-table db ( -- hash )

extra/http/server/auth/providers/db/db.factor

@@ -2,7 +2,7 @@
 ! See http://factorcode.org/license.txt for BSD license.
 USING: db db.tuples db.types accessors
 http.server.auth.providers kernel continuations
-singleton ;
+classes.singleton ;
 IN: http.server.auth.providers.db
 
 user "USERS"

extra/http/server/sessions/storage/db/db.factor

@@ -1,8 +1,8 @@
 ! Copyright (C) 2008 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: assocs accessors http.server.sessions.storage
-alarms kernel http.server db.tuples db.types singleton
-math.parser ;
+alarms kernel http.server db.tuples db.types math.parser
+classes.singleton ;
 IN: http.server.sessions.storage.db
 
 SINGLETON: sessions-in-db