Modify collapse.js unit test

The unit test would execute `hide` on an already hidden element, and
then check if it has height set (which is added by the transition). This
only worked previously, because collapse.js erroniuosly executed
`toggle` which then trigged `show` instead of `hide`. Now that `hide` is
actually executed, no transition happens, so the height value is not set
by the animation. Hence in order to test the `hide` animation, the
element must first be shown.

js/tests/unit/collapse.js

@@ -37,7 +37,7 @@ $(function () {
   })
 
   test('should hide a collapsed element', function () {
-    var $el = $('<div class="collapse"/>').bootstrapCollapse('hide')
+    var $el = $('<div class="collapse in"/>').bootstrapCollapse('hide')
 
     ok(!$el.hasClass('in'), 'does not have class "in"')
     ok(/height/i.test($el.attr('style')), 'has height set')