Adapt to upstream move of MenuItem

In I5b879c4f MenuItem was extracted to its own class.

Change-Id: I88806b9045ca7e43c13e2400970cbb0878429ce9

src/main/java/com/googlesource/gerrit/plugins/xdocs/Module.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/xdocs/Module.java b/src/main/java/com/googlesource/gerrit/plugins/xdocs/Module.java
index b90db61..ee029e3 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/xdocs/Module.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/xdocs/Module.java
@@ -18,6 +18,7 @@
 import com.google.gerrit.extensions.annotations.Exports;
 import com.google.gerrit.extensions.annotations.PluginName;
 import com.google.gerrit.extensions.client.GerritTopMenu;
+import com.google.gerrit.extensions.client.MenuItem;
 import com.google.gerrit.extensions.config.FactoryModule;
 import com.google.gerrit.extensions.registration.DynamicMap;
 import com.google.gerrit.extensions.registration.DynamicSet;