add missing docs for -e and -r options

--- a/builtins/ulimit.def
+++ b/builtins/ulimit.def
@@ -24,7 +24,7 @@
 $BUILTIN ulimit
 $FUNCTION ulimit_builtin
 $DEPENDS_ON !_MINIX
-$SHORT_DOC ulimit [-SHacdfilmnpqstuvx] [limit]
+$SHORT_DOC ulimit [-SHacdefilmnpqrstuvx] [limit]
 Ulimit provides control over the resources available to processes
 started by the shell, on systems that allow such control.  If an
 option is given, it is interpreted as follows: