Build: switch from the "popular" browser set to "popular-qunit"
Build: switch from the "popular" browser set to "popular-qunit"

jQuery is moving toward future removal of support for IE6/7, Opera 12.1x
and Safari 5.1 whereas QUnit continues to support them. This commit switches
the used browser set to one containing all those browsers.

qunitjs/qunit,qunitjs/qunit