resource_bundle_mac_unittest.mm: fix case for AppKit/AppKit.h

in SDK, it is AppKit.framework/Versions/C/Headers/AppKit.h.
Use the same case, so it would work on case sensitive filesystem.

BUG=

Review URL: https://codereview.chromium.org/1454113004

Cr-Commit-Position: refs/heads/master@{#361259}

ui/base/resource/resource_bundle_mac_unittest.mm

@@ -4,7 +4,7 @@
 
 #include "ui/base/resource/resource_bundle.h"
 
-#import <Appkit/Appkit.h>
+#import <AppKit/AppKit.h>
 
 #include "base/base_paths.h"
 #include "base/big_endian.h"