Build: Don't assume the browser environment; smoke test on Node w/ jsdom

Fixes gh-1950
@jaubourg They require `jsdom` presence, though and some people may have a problem with that (see my comment: https://github.com/jquery/jquery/pull/1949#issuecomment-67885239). I'm not sure if we have a perfect solution here without `optionalDevDependencies` but that's just one thing to consider.