Fix spring-loaded highlight on JB.

It was setting the panel to black when highlighting a CellLayout,
instead of just adding a white border.

Bug: 27135377
Change-Id: I879b12613b0cbfdda2a980065c66ea3ceb960f33
diff --git a/res/drawable/bg_celllayout.xml b/res/drawable/bg_celllayout.xml
index 651ae52..d2219b3 100644
--- a/res/drawable/bg_celllayout.xml
+++ b/res/drawable/bg_celllayout.xml
@@ -30,6 +30,7 @@
             <stroke
                 android:width="@dimen/spring_loaded_panel_border"
                 android:color="@color/spring_loaded_highlighted_panel_border_color" />
+            <solid android:color="@android:color/transparent" />
         </shape>
     </item>