shift/meta key issue fixed

js/impress.js

@@ -702,6 +702,11 @@
         //   as another way to moving to next step... And yes, I know that for the sake of
         //   consistency I should add [shift+tab] as opposite action...
         document.addEventListener("keyup", function ( event ) {
+
+            if ( event.shiftKey || event.altKey || event.ctrlKey || event.metaKey ){
+                return;
+            }
+            
             if ( event.keyCode === 9 || ( event.keyCode >= 32 && event.keyCode <= 34 ) || (event.keyCode >= 37 && event.keyCode <= 40) ) {
                 switch( event.keyCode ) {
                     case 33: // pg up