Fix Node.js 14 logical OR assignment compatibility.

Author: davidlehn

lib/deferred.js

@@ -6,7 +6,9 @@ export function deferred(f) {
       onfulfilled,
       onrejected
     ) {
-      promise ||= new Promise(resolve => resolve(f()));
+      // Use logical OR assignment when Node.js 14.x support is dropped
+      //promise ||= new Promise(resolve => resolve(f()));
+      promise || (promise = new Promise(resolve => resolve(f())));
       return promise.then(
         onfulfilled,
         onrejected