Corrected missing polyfill resources -
* Excanvas and selectorvizr was missing from polyfill directory. Since yepnope has a 10000 millisecond resource timeout, this created a 20000 millisecond lag for all other tests and in Modernizr
* Corrects the lag notice by @pjackson in PR #2978
Merge pull request #2980 from masterbee/hotfix--missingpolyfils

Corrected missing polyfill resources -
Jaws polyfill: Added polyfill to fix the Jaws sectioning elements/heading level incrementation bug and the sectioning element/heading association bug.