fix id (#4639)

packages/app/src/components/PageTimeline.jsx

@@ -76,14 +76,14 @@ class PageTimeline extends React.Component {
       <div>
         { pages.map((page) => {
           return (
-            <div className="timeline-body" key={`key-${page.id}`}>
+            <div className="timeline-body" key={`key-${page._id}`}>
               <div className="card card-timeline">
                 <div className="card-header"><a href={page.path}>{page.path}</a></div>
                 <div className="card-body">
                   <RevisionLoader
                     lazy
                     growiRenderer={this.growiRenderer}
-                    pageId={page.id}
+                    pageId={page._id}
                     revisionId={page.revision}
                   />
                 </div>