GUACAMOLE-1859: Update to latest compatible versions of JavaScript dependencies.

The Pickr library also has an update (v1.9.0), but that update does not
successfully build, possibly due to a different level of JavaScript
version compatibility.

doc/licenses/webpack-4.47.0/README

@@ -0,0 +1,8 @@
+Webpack (https://webpack.js.org/)
+---------------------------------
+
+    Version: 4.47.0
+    From: 'JS Foundation and other contributors'
+    License(s):
+        MIT (bundled/webpack-4.47.0/LICENSE)
+