fix: ensure that Karma supports running tests on IE 11 (#3642)

They were failing because of unsupported arrow function syntax in two places:
- in karma.spec.js file (only affecting Karma's own tests)
- in socket.io.js file installed from NPM, hence the dependency update (this affected Karma consumers)

Enabled BrowserStack tests on IE 11 to prevent regressions.

package.json

@@ -428,7 +428,7 @@
     "qjobs": "^1.2.0",
     "range-parser": "^1.2.1",
     "rimraf": "^3.0.2",
-    "socket.io": "^3.0.4",
+    "socket.io": "^3.1.0",
     "source-map": "^0.6.1",
     "tmp": "0.2.1",
     "ua-parser-js": "^0.7.23",

test/client/karma.conf.js

@@ -14,35 +14,20 @@ const launchers = {
     browser: 'firefox',
     os: 'Windows',
     os_version: '10'
-  }
+  },
   // bs_safari: {
   //   base: 'BrowserStack',
-  //   browser: 'safari',
-  //   browser_version: '9.0',
-  //   os_version: 'El Capitan',
-  //   os: 'OS X'
-  // },
-  // bs_ie_11: {
-  //   base: 'BrowserStack',
-  //   browser: 'ie',
-  //   browser_version: '11.0',
-  //   os: 'Windows',
-  //   os_version: '10'
-  // },
-  // bs_ie_10: {
-  //   base: 'BrowserStack',
-  //   browser: 'ie',
-  //   browser_version: '10.0',
-  //   os: 'Windows',
-  //   os_version: '8'
+  //   browser: 'Safari',
+  //   os: 'OS X',
+  //   os_version: 'Big Sur'
   // },
-  // bs_ie_9: {
-  //   base: 'BrowserStack',
-  //   browser: 'ie',
-  //   browser_version: '9.0',
-  //   os: 'Windows',
-  //   os_version: '7'
-  // }
+  bs_ie: {
+    base: 'BrowserStack',
+    browser: 'IE',
+    browser_version: '11.0',
+    os: 'Windows',
+    os_version: '10'
+  }
 }
 
 // Verify the install. This will run async but that's ok we'll see the log.

test/client/karma.spec.js

@@ -17,7 +17,7 @@ describe('Karma', function () {
   beforeEach(function () {
     mockTestStatus = ''
     updater = {
-      updateTestStatus: (s) => {
+      updateTestStatus: function (s) {
         mockTestStatus = s
       }
     }
@@ -454,7 +454,7 @@ describe('Karma', function () {
       clock.tick(500)
 
       ck.complete()
-      setTimeout(() => {
+      setTimeout(function () {
         assert(windowLocation.href === 'http://return.com')
         done()
       }, 5)