PLT-126: Change 'Private Messages' to 'Direct Messages'

Signed-off-by: Chengwei Yang <yangchengwei@qiyi.com>

web/react/components/rhs_root_post.jsx

@@ -53,7 +53,7 @@ export default class RhsRootPost extends React.Component {
         var channelName;
         if (channel) {
             if (channel.type === 'D') {
-                channelName = 'Private Message';
+                channelName = 'Direct Message';
             } else {
                 channelName = channel.display_name;
             }