hush: make "true" built-in

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush.c b/shell/hush.c
index 9271934..7b0ea8b 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -944,6 +944,7 @@
 	BLTIN("source"   , builtin_source  , "Run commands in a file"),
 #endif
 	BLTIN("trap"     , builtin_trap    , "Trap signals"),
+	BLTIN("true"     , builtin_true    , NULL),
 	BLTIN("type"     , builtin_type    , "Show command type"),
 	BLTIN("ulimit"   , shell_builtin_ulimit  , "Control resource limits"),
 	BLTIN("umask"    , builtin_umask   , "Set file creation mask"),