fix wrong definition for metaFields property (#1763)

* fix wrong definition for metaFields property

* dashboard: add type test for metaFields

packages/@uppy/dashboard/types/dashboard-tests.ts

@@ -15,9 +15,13 @@ import Dashboard = require('../')
 
 {
   const uppy = Uppy()
-  uppy.use(Dashboard, {
+  uppy.use(Dashboard, <Partial<Dashboard.DashboardOptions>>{
     width: '100%',
-    height: 700
+    height: 700,
+    metaFields: [
+      { id: 'caption', name: 'Caption' },
+      { id: 'license', name: 'License', placeholder: 'Creative Commons, Apache 2.0, ...' },
+    ]
   })
 }
 

packages/@uppy/dashboard/types/index.d.ts

@@ -1,5 +1,11 @@
 import Uppy = require('@uppy/core');
 
+interface MetaField {
+  id: string;
+  name: string;
+  placeholder?: string;
+}
+
 declare module Dashboard {
   interface DashboardOptions extends Uppy.PluginOptions {
     onRequestCloseModal: () => void;
@@ -14,7 +20,7 @@ declare module Dashboard {
     note: string;
     showLinkToFileUploadResult: boolean;
     proudlyDisplayPoweredByUppy: boolean;
-    metaFields: string[];
+    metaFields: MetaField[];
     plugins: string[];
     disableStatusBar: boolean;
     showProgressDetails: boolean;