Fix shouldDiscard example

Author: Abhayaj247

src/webgl/ShaderGenerator.js

@@ -1885,8 +1885,7 @@ if (typeof p5 !== 'undefined') {
  *   createCanvas(200, 200, WEBGL);
  *   myShader = baseStrokeShader().modify(() => {
  *     shouldDiscard(willDiscard => {
- *       // Discard fragments based only on the default logic
- *       return willDiscard;
+ *       'bool shouldDiscard': '(bool outside) { return outside; }'
  *   });
  * }
  * function draw() {