Fixed React warnings

app/components/Collaborators/Collaborators.js

@@ -29,8 +29,8 @@ const Collaborators = ({ document }: Props) => {
     <Avatars>
       <StyledTooltip tooltip={tooltip} placement="bottom">
         {collaborators.map(user => (
-          <AvatarWrapper>
-            <Avatar key={user.id} src={user.avatarUrl} />
+          <AvatarWrapper key={user.id}>
+            <Avatar src={user.avatarUrl} />
           </AvatarWrapper>
         ))}
       </StyledTooltip>

app/components/DocumentPreview/DocumentPreview.js

@@ -98,13 +98,13 @@ class DocumentPreview extends Component {
         <h3>
           <Highlight text={document.title} highlight={highlight} />
           {document.starred ? (
-            <a onClick={this.unstar}>
+            <span onClick={this.unstar}>
               <StyledStar solid />
-            </a>
+            </span>
           ) : (
-            <a onClick={this.star}>
+            <span onClick={this.star}>
               <StyledStar />
-            </a>
+            </span>
           )}
         </h3>
         <PublishingInfo