chore(ci): re-enable tests on Windows (#5637)

* chore: Add Windows to Travis

This commit runs the unit tests on Windows.

There are two tests failing on Windows that we skip.

I spoke to Mathias B and we agreed to
defer debugging this for now in favour of getting tests running on
Windows. But we didn't want to ignore it forever, hence giving the test
a date at which it will start to fail.

test/mocha-utils.js

@@ -17,6 +17,7 @@
 const {TestServer} = require('../utils/testserver/index');
 const path = require('path');
 const fs = require('fs');
+const os = require('os');
 const puppeteer = require('../');
 const utils = require('./utils');
 const assertCoverage = require('./coverage-utils');
@@ -92,6 +93,15 @@ global.itFailsFirefox = (...args) => {
     return it(...args);
 };
 
+global.itFailsWindowsUntilDate = (date, ...args) => {
+  if (os.platform() === 'win32' && Date.now() < date) {
+    // we are within the deferred time so skip the test
+    return xit(...args);
+  }
+
+  return it(...args);
+};
+
 global.describeFailsFirefox = (...args) => {
   if (isFirefox)
     return xdescribe(...args);