Fix spin function syntax for Svelte tutorial auto-grader (#626)

Corrected arrow function syntax to include missing parenthesis around the "t" parameter and added semicolon after the last backtick in returned CSS string. The auto-grader expects both.

content/tutorial/02-advanced-svelte/02-transitions/04-custom-css-transitions/README.md

@@ -53,7 +53,7 @@ We can get a lot more creative though. Let's make something truly gratuitous:
  function spin(node, { duration }) {
  return {
  duration,
- css: t => +++{
+ css: (t) => +++{
  const eased = elasticOut(t);
 
  return `
@@ -62,7 +62,7 @@ We can get a lot more creative though. Let's make something truly gratuitous:
  ${Math.trunc(t * 360)},
  ${Math.min(100, 1000 * (1 - t))}%,
  ${Math.min(50, 500 * (1 - t))}%
- );`
+ );`;
  }+++
  };
  }