Update qunit submodule from 1.3.0pre to 1.6.0pre, close gh-761

- See also: https://github.com/jquery/qunit/blob/master/History.md

diff --git a/test/qunit b/test/qunit
index 0712230bb203c262211649b32bd712ec7df5f857..74cc047c61507395b36db7065231572852f6d19d 160000 (submodule)
--- a/test/qunit
+++ b/test/qunit
@@ -1 +1 @@
-Subproject commit 0712230bb203c262211649b32bd712ec7df5f857
+Subproject commit 74cc047c61507395b36db7065231572852f6d19d