Fixes an accidental change made to WebKit GTK code.

This was made in change 95e3d862bbab761f8caaf1d1b54065f67b9a5148.
See https://android-git.corp.google.com/w/?p=platform/external/webkit.git;a=commitdiff;h=95e3d862bbab761f8caaf1d1b54065f67b9a5148#patch1

This will help avoid noise in the diffs when upstreaming Android-specific changes to webkit.org.
diff --git a/WebCore/platform/DragImage.h b/WebCore/platform/DragImage.h
index 0196971..4887066 100644
--- a/WebCore/platform/DragImage.h
+++ b/WebCore/platform/DragImage.h
@@ -71,7 +71,7 @@
 #elif PLATFORM(WX)
     typedef wxDragImage* DragImageRef;
 #elif PLATFORM(GTK)
-    typedef GdkPixBuf* DragImageRef;
+    typedef GdkPixbuf* DragImageRef;
 #elif PLATFORM(ANDROID)
     typedef void* DragImageRef;
 #endif