Fix map example

Author: PalumboN

src/math/calculation.js

@@ -574,7 +574,7 @@ p5.prototype.mag = function(x, y) {
  *   let x = map(mouseX, 0, 100, 0, 50);
  *
  *   // Draw the bottom line.
- *   line(0, 75, 0, x);
+ *   line(0, 75, x, 75);
  * }
  * </code>
  * </div>