Adapt to AccountGroup.UUID refactoring

Change-Id: Ie227ccbf5ce72275dafe4a1e9a9865bcc521bc34

src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java b/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
index 20538b9..93daf4d 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
@@ -170,7 +170,7 @@
   }
 
   private static AccountGroup.UUID uuid(String username) {
-    return new AccountGroup.UUID(UUID_PREFIX + username);
+    return AccountGroup.uuid(UUID_PREFIX + username);
   }
 
   private static void checkUUID(AccountGroup.UUID uuid) {