use ALT as hotkey modifier

lib/scripts/hotkeys.js

@@ -18,7 +18,7 @@ function Hotkeys() {
      *  this.modifier = 'alt';
      *  this.modifier = 'alt+shift';
      */
-    this.modifier = 'ctrl';
+    this.modifier = 'alt';
 
     /**
      * Initialization
@@ -288,4 +288,4 @@ function Hotkeys() {
 function initializeHotkeys() {
     var hotkeys = new Hotkeys();
     hotkeys.initialize();
-}
\ No newline at end of file
+}