So this is a little self serving, but I think we should consider dropping support for IE9.  The data is interesting.  I'm seeing a [0.6% browser market share for IE9](https://netmarketshare.com/browser-market-share.aspx?options=%7B%22filter%22%3A%7B%22%24and%22%3A%5B%7B%22deviceType%22%3A%7B%22%24in%22%3A%5B%22Desktop%2Flaptop%22%5D%7D%7D%5D%7D%2C%22dateLabel%22%3A%22Trend%22%2C%22attributes%22%3A%22share%22%2C%22group%22%3A%22browserVersion%22%2C%22sort%22%3A%7B%22share%22%3A-1%7D%2C%22id%22%3A%22browsersDesktopVersions%22%2C%22dateInterval%22%3A%22Monthly%22%2C%22dateStart%22%3A%222017-07%22%2C%22dateEnd%22%3A%222018-06%22%2C%22segments%22%3A%22-1000%22%2C%22pageLength%22%3A50%7D).

What's neat about that data is that IE8 has twice the usage of IE9 🤷‍♂️ And IE10 has only 0.54% market share!  I could make a reasonable argument for dropping both IE9 *and* IE10.  

Of course, I'm only looking at this because I'd very much like to ship a new npm module with a few recently merged changes, and the IE9 tests are failing :)  

What are folks thoughts?  Does anyone feel strongly about the IE support matrix as it stands today?

@nickuraltsev @mzabriskie 
test/specs/requests.spec.js
request.respondWith({
        status: 500
      });
    });
  });
  it('should resolve when validateStatus returns true', function (done) {
    var resolveSpy = jasmine.createSpy('resolve');
    var rejectSpy = jasmine.createSpy('reject');
    axios('/foo', {
      validateStatus: function (status) {
        return status === 500;
      }
    }).then(resolveSpy)
      .catch(rejectSpy)
      .then(function () {
        expect(resolveSpy).toHaveBeenCalled();
        expect(rejectSpy).not.toHaveBeenCalled();
        done();
      });
    getAjaxRequest().then(function (request) {
      request.respondWith({
        status: 500
      });
    });
  });
  
  it('should return JSON when rejecting', function (done) {
    var response;
    axios('/api/account/signup', {
      username: null,