Fix RTL unit tests for jQuery 3.3.1

In PhantomJS, .css('right') in jQuery 2.1.1 returns a string as a percentage (%).
In PhantomJS, .css('right') in jQuery 3.3.1 returns a string in pixels (px).
For other browsers (Chrome, Firefox, IE), .css('right') in jQuery 2.1.1
returns a string in pixels (px).

Author: jespirit

test/specs/RtlOptionsSpec.js

@@ -49,7 +49,7 @@ describe("RTL Tests", function() {
       var sliderTrackHighLeft=$("#rtlSlider").siblings(".slider-rtl").children("div.slider-track").children("div.slider-track-high").css("left");
 
       expect(sliderTrackLowRight).toBe("0px");
-      expect(sliderSelectionRight).toBe("0%");
+      expect(sliderSelectionRight).toBe("0px");
       expect(sliderTrackHighLeft).toBe("0px");
     });