Fix Array to string conversion

[PhiloNL]

If you try to render a multi-level array it will throw an Array to string conversion exception.

[
    'example' => ['name' => 'test', 'address' => []]
];

{{  example }}

This will recursively implode the array.

• I've run the tests with vendor/bin/phpunit
• None of the tests were found failing
• I've seen the coverage report at build/coverage/index.html
• Not a single line left uncovered by tests
• Any coding standards issues were fixed with vendor/bin/php-cs-fixer fix