refactor: use async/await for subdoc post save

lib/plugins/saveSubdocs.js

@@ -58,31 +58,41 @@ module.exports = function saveSubdocs(schema) {
     await Promise.all(promises);
   });
 
-  schema.s.hooks.post('save', function saveSubdocsPostSave(doc, next) {
+  schema.s.hooks.post('save', async function saveSubdocsPostSave() {
     if (this.$isSubdocument) {
-      next();
       return;
     }
 
     const _this = this;
     const subdocs = this.$getAllSubdocs();
 
     if (!subdocs.length) {
-      next();
       return;
     }
 
-    each(subdocs, function(subdoc, cb) {
-      subdoc.$__schema.s.hooks.execPost('save', subdoc, [subdoc], function(err) {
-        cb(err);
-      });
-    }, function(error) {
-      if (error) {
-        return _this.$__schema.s.hooks.execPost('save:error', _this, [_this], { error: error }, function(error) {
-          next(error);
+    const promises = [];
+    for (const subdoc of subdocs) {
+      promises.push(new Promise((resolve, reject) => {
+        subdoc.$__schema.s.hooks.execPost('save', subdoc, [subdoc], function(err) {
+          if (err) {
+            return reject(err);
+          }
+          resolve();
         });
-      }
-      next();
-    });
+      }));
+    }
+
+    try {
+      await Promise.all(promises);
+    } catch (error) {
+      await new Promise((resolve, reject) => {
+        this.$__schema.s.hooks.execPost('save:error', _this, [_this], { error: error }, function(error) {
+          if (error) {
+            return reject(error);
+          }
+          resolve();
+        });
+      });
+    }
   }, null, unshift);
 };