Respect coding standard in documentation

[VincentLanglet]

From https://twig.symfony.com/doc/3.x/coding_standards.html

Put exactly one space after the : sign in hashes and , in arrays and hashes:
{{ [1, 2, 3] }}
{{ {'foo': 'bar'} }}

Do not put any spaces before and after the opening and the closing of arrays and hashes:
{{ [1, 2, 3] }}
{{ {'foo': 'bar'} }}

[fabpot]

Thank you @VincentLanglet.