Fix one pixel difference of Exclusive checkbox

Exclusive checkbox of project access rights is not in the same column as others checkboxes are (http://snag.gy/YNGRN.jpg).

Change-Id: I67a5b5bf360799764fc951da960885b4b7b3b54e
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/PermissionEditor.ui.xml b/gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/PermissionEditor.ui.xml
index 25995d9..ada070d 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/PermissionEditor.ui.xml
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/PermissionEditor.ui.xml
@@ -39,6 +39,7 @@
   }
 
   .header {
+    position: relative;
     padding-left: 5px;
     padding-right: 5px;
     padding-bottom: 1px;