Fix selector that hides Documentation link

The selector was not specific enough, so the link was not getting
hidden.

Change-Id: I5aeacd4c4791bd556bba0f7075ae0c0a24b4a8db
diff --git a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.html b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.html
index a3c6bb7..04db296 100644
--- a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.html
+++ b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.html
@@ -121,7 +121,7 @@
         }
         gr-search-bar,
         .browse,
-        li.hideOnMobile {
+        .links > li.hideOnMobile {
           display: none;
         }
         .accountContainer {