Refactor KawaiiGherkin\Formatter\Example::format method's return.

[jackmakiyama]

The file src/Formatter/Example.php have a comment recommending refactoring the return method of KawaiiGherkin\Formatter\Example::format class:

// TODO: refactor this part
        return implode(
            array_merge(
                [
                    $this->indent(self::INDENTATION * 2) . rtrim($scenario->getExampleTable()->getKeyword()) . ":\n",
                ],
                array_map(
                    function ($arguments) {
                        return $this->indent(self::INDENTATION * 2 + 2) . trim($arguments) . "\n";
                    },
                    explode("\n", $scenario->getExampleTable()->getTableAsString())
                )
            )
        );

I removed this comment in PR #7.