Update jquery.nicescroll.js

`tabindex` must be `0` to keep natural tabbing flow.

http://snook.ca/archives/accessibility_and_usability/elements_focusable_with_tabindex

jquery.nicescroll.js

@@ -22,7 +22,7 @@
   var domfocus = false;
   var mousefocus = false;
   var zoomactive = false;
-  var tabindexcounter = 5000;
+  var tabindexcounter = 0;
   var ascrailcounter = 2000;
   var globalmaxzindex = 0;
   
@@ -3250,4 +3250,4 @@
   }
   
 }));
-  
+