Use es5-ext/global as a more robust way to resolve browser's window

The [es5-ext/global][es5g] module is based on Mathias Bynens' [polyfill][poly]
for [`globalThis`][gT]. It uses the same robust technique but is more
conservative in that it does not add a `globalThis` property to the resolved
object, i.e. `window` in a browser and `global` in Node. It also lacks the "old
IE" fallback seen in a [demo][demo] of the original polyfill, but that is
easily provided in this commit.

[es5g]: https://github.com/medikoo/es5-ext/blob/master/global.js
[poly]: https://mathiasbynens.be/notes/globalthis
[gT]: https://github.com/tc39/proposal-global
[demo]: https://mathiasbynens.be/demo/globalthis-ie

lib/browser.js

@@ -1,10 +1,13 @@
-var _global = (function () {
-	if (!this && typeof global !== 'undefined') {
-		return global;
-	}
-	return this;
-})();
-var NativeWebSocket = _global.WebSocket || _global.MozWebSocket;
+var _globalThis;
+try {
+	_globalThis = require('es5-ext/global');
+} catch (error) {
+} finally {
+	if (!_globalThis && typeof window !== 'undefined') { _globalThis = window; }
+	if (!_globalThis) { throw new Error('Could not determine global this'); }
+}
+
+var NativeWebSocket = _globalThis.WebSocket || _globalThis.MozWebSocket;
 var websocket_version = require('./version');
 
 

package.json

@@ -28,6 +28,7 @@
   },
   "dependencies": {
     "debug": "^2.2.0",
+    "es5-ext": "^0.10.50",
     "nan": "^2.14.0",
     "gulp": "^4.0.2",
     "typedarray-to-buffer": "^3.1.5",