fix: required scripts loading race condition

Author: peterpeterparker

webcomponents/highlight-code/CHANGELOG.md

@@ -8,6 +8,7 @@
 
 - support alias (such as `html` for `markup`)
 - load alias required scripts
+- required scripts loading race condition
 
 # 2.2.1 (2020-11-19)
 

webcomponents/highlight-code/src/components/highlight-code/deckdeckgo-highlight-code.tsx

@@ -227,7 +227,7 @@ export class DeckdeckgoHighlightCode {
 
       document.head.appendChild(script);
 
-      resolve();
+      script.addEventListener('load', () => resolve(), {once: true});
     });
   }