Fixed failing test for VideoAlpha caption heiht.

It turns out that there was wrong invocation of toBeCloseTo() function. Most likely a typo.
Updated the readme.

common/lib/xmodule/xmodule/js/spec/videoalpha/readme.md

 Jasmine JavaScript tests status
 -------------------------------
 
-As of 22.07.2013, all the tests in this directory pass. To disable each of them, change the top level "describe(" to "xdescribe(".
+As of 22.07.2013, all the tests in this directory pass. To enable a test file, change
+the top level "xdescribe(" to "describe(".
 
 PS: When you are running the tests in chrome locally, make sure that chrome is started
 with the option "--allow-file-access-from-files".

common/lib/xmodule/xmodule/js/spec/videoalpha/video_caption_spec.js

@@ -368,16 +368,15 @@
           expect(realHeight).toBeCloseTo(shouldBeHeight, 2);
         });
 
-        xit('when CC button is disabled ', function() {
+        it('when CC button is disabled ', function() {
           var realHeight = parseInt($('.subtitles').css('maxHeight'), 10),
               videoWrapperHeight = $('.video-wrapper').height(),
-              controlsHeight = videoControl.el.height(),
               progressSliderHeight = videoControl.sliderEl.height(),
-              shouldBeHeight = videoWrapperHeight - controlsHeight - 0.5 * controlsHeight;
+              shouldBeHeight = videoWrapperHeight - 0.5 * progressSliderHeight;
 
           state.captionsHidden = true;
           videoCaption.setSubtitlesHeight();
-          expect(realHeight).toBeCloseTo($('.video-wrapper').height(shouldBeHeight, 2));
+          expect(realHeight).toBeCloseTo(shouldBeHeight, 2);
         });
       });