Fix AudioEffectFlange documentation

https://forum.pjrc.com/threads/32580-Audio-System-Design-Tool-Typo

gui/index.html

@@ -1757,7 +1757,7 @@ The actual packets are taken
 	the modulation depth (larger values give a greater variation) and the modulation
 	frequency, in Hertz.
 	</p>
-	<p class=func><span class=keyword>modify</span>(offset, depth, delayRate);</p>
+	<p class=func><span class=keyword>voices</span>(offset, depth, delayRate);</p>
 	<p class=desc>Alters the parameters in a running flanger (previously started with begin).
 	</p>