make ExpressionLanguage/FunctionsProvider/Typo3ConditionFunctionsProvider.php symfony expression function provider interface compatible

[Alexander Grein]

The interface requires, that the getFunctions method returns an array.

public function getFunctions()

Should be

public function getFunctions(): array

[David Bascom]

https://bitbucket.org/99grad/nnhelpers/commits/9192f0b605f0f808e49ac87f3ec5c7fc3fdaafca