Fix bug on pages with predefined canvas background color

In some pages with predefined canvas background color for canvas element like the website of the [Foundation framework](http://foundation.zurb.com/whats-new.php), script stopped working and only shows a colored canvas, I have fixed this issue by adding transparent background to the element, but because I dont know which js compressor is used to compress js file and build fokus.min.js, I dont changed it, so if you want to push my changes to your repository, please build that file first.