Fix shadow in DisplayStyleDrawer Theme.

[Yeti-or]

When you use DisplayStyleDrawer theme for first time the shadow of masterView is not hidden.

BDBSplitViewController *splitViewController = [[BDBSplitViewController alloc] initWithMasterViewController:[MasterViewController new]
                                                                                      detailViewController:[[DrawerDetailViewController alloc] initWithNibName:nil bundle:nil]];

Before:

After:

[bdbergeron]

Due to other changes I made during development of 1.3.0, this issue is now resolved. Thanks!