Issue #3303686: External library definition

lightning_scheduler.libraries.yml

 react:
   js:
     'https://unpkg.com/react@16.3.2/umd/react.production.min.js':
-      external: true
+      type: external
       attributes:
         integrity: 'sha384-ssmDfleGSKwIS4GlKJM3gqgSQtp6pzFAc7y8f0r2Mfjn+EsHt4UqrSM8EXKZCAFU'
         crossorigin: anonymous
     'https://unpkg.com/react-dom@16.3.2/umd/react-dom.production.min.js':
-      external: true
+      type: external
       attributes:
         integrity: 'sha384-9HNXemlU8cB7vTVvdlZbsut+fnt78jK2amX1CCxkLlamx+yD4gde8D6DJe+QkHm3'
         crossorigin: anonymous