Cocoa: Disable shadow for transparent framebuffer

src/cocoa_window.m

@@ -868,6 +868,7 @@ static GLFWbool createNativeWindow(_GLFWwindow* window,
     if (fbconfig->transparent)
     {
         [window->ns.object setOpaque:NO];
+        [window->ns.object setHasShadow:NO];
         [window->ns.object setBackgroundColor:[NSColor clearColor]];
     }