worker: have terminate return a promise.

See: nodejs/node#28021

Author: chjj

lib/browser/worker.js

@@ -262,14 +262,19 @@ class Worker extends EventEmitter {
     });
   }
 
-  terminate(callback) {
+  async terminate(callback) {
     if (this._exited)
       return;
 
     if (typeof callback === 'function')
       this.once('exit', code => callback(null, code));
 
     this._terminate(1);
+
+    // See: https://github.com/nodejs/node/pull/28021
+    return new Promise((resolve) => {
+      this.once('exit', resolve);
+    });
   }
 
   unref() {

lib/process/worker.js

@@ -638,14 +638,19 @@ class Worker extends EventEmitter {
     this._exited = true;
   }
 
-  terminate(callback) {
+  async terminate(callback) {
     if (this._exited)
       return;
 
     if (typeof callback === 'function')
       this.once('exit', code => callback(null, code));
 
     this._terminate(1);
+
+    // See: https://github.com/nodejs/node/pull/28021
+    return new Promise((resolve) => {
+      this.once('exit', resolve);
+    });
   }
 
   unref() {