message: docs(marble-testing): fix typo in marble testing docs
  replace 'output' with 'expected' in Time Progression Syntax section
diff: @@ -69,15 +69,15 @@ When it's not the first character of the diagram it must be padded a space befor
  ```ts
  const input = ' -a-b-c|';
  -const output = '-- 9ms a 9ms b 9ms (c|)';
  +const expected = '-- 9ms a 9ms b 9ms (c|)';
  /*
  // Depending on your personal preferences you could also
  // use frame dashes to keep vertical aligment with the input
  const input = ' -a-b-c|';
  -const output = '------- 4ms a 9ms b 9ms (c|)';
  +const expected = '------- 4ms a 9ms b 9ms (c|)';
  // or
  -const output = '-----------a 9ms b 9ms (c|)';
  +const expected = '-----------a 9ms b 9ms (c|)';
  */
  