Docs: Use require without brackets

[piotr-cz]

Because brackets with require is not necessary and implies it's a function, while it's a statement.

In phinx code, require is used without brackets:

phinx/app/phinx.php

Line 26 in 6f0ec12

$autoloader = require __DIR__ . '/../src/composer_autoloader.php';

phinx/app/web.php

Line 42 in 6f0ec12

$app = require __DIR__ . '/phinx.php';