extra tests for `Map`, see data-es6.js

Sorry, the compatibility data i have is only for Chrome, Firefox, IE 11.

I think it's important that the table records accurate results for every browser that is listed, all the way back to FF11. (Several other people can correct these results after the pullreq is accepted.) FF24 supports `Map#keys` but not `Map#forEach`. FF18 supports neither but does support `for...of`. (It may seem apparent that any browser predating `Map#forEach` would sure fail the test due to the SameValueZero requirement not being specced until after, but you never can be sure.)