Update index.js

Fixes dt sign when calculated automatically

Author: emersion

lib/index.js

@@ -32,7 +32,7 @@ Controller.prototype.update = function(currentValue) {
     if (this.lastTime === 0) { // First time update() is called
       dt = 1;
     } else {
-      dt = (this.lastTime - currentTime) / 1000; // in seconds
+      dt = (currentTime - this.lastTime) / 1000; // in seconds
     }
     this.lastTime = currentTime;
   }