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 
lib/adapters/xhr.js
'use strict';
var utils = require('./../utils');
var settle = require('./../core/settle');
var buildURL = require('./../helpers/buildURL');
var parseHeaders = require('./../helpers/parseHeaders');
var isURLSameOrigin = require('./../helpers/isURLSameOrigin');
var createError = require('../core/createError');
module.exports = function xhrAdapter(config) {
  return new Promise(function dispatchXhrRequest(resolve, reject) {
    var requestData = config.data;
    var requestHeaders = config.headers;
    if (utils.isFormData(requestData)) {
      delete requestHeaders['Content-Type']; 
    }
    var request = new XMLHttpRequest();
    
    if (config.auth) {
      var username = config.auth.username || '';
      var password = config.auth.password || '';
      requestHeaders.Authorization = 'Basic ' + btoa(username + ':' + password);
    }
    request.open(config.method.toUpperCase(), buildURL(config.url, config.params, config.paramsSerializer), true);
    
    request.timeout = config.timeout;