chore(travis): let's give BrowserStack a try

Switch the build to use BrowserStack instead of SauceLabs.

This also adds IE11 to our build.

lib/browser-stack/start-tunnel.js

@@ -0,0 +1,47 @@
+var fs = require('fs');
+var http = require('http');
+var BrowserStackTunnel = require('browserstacktunnel-wrapper');
+
+var HOSTNAME = 'localhost';
+var PORTS = [9090, 9876];
+var ACCESS_KEY = process.env.BROWSER_STACK_ACCESS_KEY;
+var READY_FILE = process.env.SAUCE_CONNECT_READY_FILE;
+
+// We need to start fake servers, otherwise the tunnel does not start.
+var fakeServers = [];
+var hosts = [];
+
+PORTS.forEach(function(port) {
+  fakeServers.push(http.createServer(function() {}).listen(port));
+  hosts.push({
+    name: HOSTNAME,
+    port: port,
+    sslFlag: 0
+  });
+});
+
+var tunnel = new BrowserStackTunnel({
+  key: ACCESS_KEY,
+  hosts: hosts
+});
+
+
+tunnel.start(function(error) {
+  console.log('** callback **')
+  if (error) {
+    console.error('Can not establish the tunnel', error);
+  } else {
+    console.log('Tunnel established.');
+    fakeServers.forEach(function(server) {
+      server.close();
+    });
+
+    if (READY_FILE) {
+      fs.writeFile(READY_FILE, '');
+    }
+  }
+});
+
+tunnel.on('error', function(error) {
+  console.error(error);
+});

lib/browser-stack/start-tunnel.sh

@@ -0,0 +1 @@
+node ./lib/browser-stack/start-tunnel.js &