[List.pod] inserted missing commas

For some reason, if 'comma' were pluralized 'commae', I wouldn't
be too surprised. It isn't, of course. But still.

Author: Carl Mäsak

lib/List.pod

@@ -242,8 +242,8 @@ and C<redo> statements.
 
 =head2 splice
 
-    multi sub    splice(@list,  $start, $elems? *@replacement) returns List:D
-    multi method splice(List:D: $start, $elems? *@replacement) returns List:D
+    multi sub    splice(@list,  $start, $elems?, *@replacement) returns List:D
+    multi method splice(List:D: $start, $elems?, *@replacement) returns List:D
 
 Deletes C<$elems> elements starting from index C<$start> from the list,
 returns them and replaces them by C<@replacement>. If C<$elems> is omitted,