fix(stark-starter): add polyfill for String.prototype.trimRight

IE11 required a polyfill for `String.prototype.trimRight`, this function was used by the `prettier`
dependency and caused an issue when using the `pretty-print` component.

ISSUES CLOSED: NationalBankBelgium#213

starter/src/polyfills.browser.ts

@@ -71,6 +71,11 @@ import "zone.js/dist/zone";
 /***************************************************************************************************
  * APPLICATION IMPORTS
  */
+/**
+ * IE11 requires a polyfill for trimRight (used by prettier library)
+ * see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trimEnd#Browser_compatibility
+ */
+import "core-js/modules/es7.string.trim-right";
 
 /* tslint:disable:no-all-duplicated-branches */
 if ("production" === ENV) {