Added test for addClassesToSVGElement (currently failing).

[keeganstreet]

Added test for addClassesToSVGElement to demonstrate that this plugin is currently failing.

  1) plugins tests
       addClassesToSVGElement.01:

      AssertionError: expected '<svg xmlns="http://www.w3.org/2000/svg" class="">\n    test\n</svg>' to be '<svg xmlns="http://www.w3.org/2000/svg" class="mySvg size-big">\n    test\n</svg>'
      + expected - actual

      -<svg xmlns="http://www.w3.org/2000/svg" class="">
      +<svg xmlns="http://www.w3.org/2000/svg" class="mySvg size-big">
           test
       </svg>

[strarsis]

@keeganstreet: With #592 Element.classList property support has been added.
Using it in plugin should make the plugin much, much simpler and also fix this issue.

[GreLI]

Thanks to both for your attention! Fixed in b51192c.