Add mutation/resolver for multi file upload

api/resolvers.js

@@ -8,6 +8,10 @@ export default {
     singleUpload (root, {file}) {
       console.log('Uploaded file:', file)
       return file
+    },
+    multiUpload (root, {files}) {
+      console.log('Uploaded files:', files)
+      return files
     }
   }
 }

api/schema.graphql

@@ -19,4 +19,5 @@ type Query {
 
 type Mutation {
   singleUpload (file: Upload!): File!
+  multiUpload (files: [Upload!]): [File!]
 }