pixels tutorial: fix float cast sytax error

* requested by #165

Author: FeXd

Tutorials/pixels/index.html

@@ -355,7 +355,7 @@ <h3>Our second image filter, making our own "tint"</h3>
         b = blue(img.pixels[loc])
 
         # Change brightness according to the mouse here
-        adjustBrightness = ((float) mouseX / width) * 8.0
+        adjustBrightness = (float(mouseX) / width) * 8.0
         r *= adjustBrightness
         g *= adjustBrightness
         b *= adjustBrightness