only include isomorphic-fetch if the application has explicitly disab…

…led native fetch

this will allow us to gradually enable native fetch in apps without a breaking change.

main.js

@@ -6,7 +6,13 @@
  * @typedef {import("./typings/metrics").TickingMetric} TickingMetric
  */
 
-require('isomorphic-fetch');
+// only include isomorphic-fetch if the application has explicitly disabled native fetch
+if(
+	process.allowedNodeEnvironmentFlags.has('--no-experimental-fetch') && 
+	process.execArgv.includes('--no-experimental-fetch')
+) {
+	require('isomorphic-fetch');
+}
 
 const fs = require('fs');
 const path = require('path');