Update app.js

Fix: If angular-filemanager was embedded in some other parent div (e.g. bootstrap modal) with CSS position absolute or relative, then the position of contextmenu would be wrong.

Author: liul

src/js/app.js

@@ -28,7 +28,7 @@
         menu.hide().css({
             left: e.pageX,
             top: e.pageY
-        }).show();
+        }).appendTo('body').show();
         e.preventDefault();
     });