Update webgl_volume_perlin.html

Optimize refinement steps.

examples/webgl_volume_perlin.html

@@ -127,7 +127,7 @@
 					uniform float steps;
 					uniform bool refine;
 
-					#define REFINEMENT_STEPS 6
+					#define REFINEMENT_STEPS 4
 
 					vec2 hitBox( vec3 orig, vec3 dir ) {
 						const vec3 box_min = vec3( - 0.5 );