Merge pull request #3930 from floriantraber/bug/3571-oas-3.0-doesnt-render-in-ie11-startsWith-function-missing

Fixes #3571 - add polyfill for startsWith function for IE11.

src/polyfills.js

@@ -3,3 +3,8 @@
 if(!window.Promise) {
   require("core-js/fn/promise")
 }
+
+// Required by IE 11
+if(!String.prototype.startsWith) {
+  require("core-js/es6/string")
+}