Using ArrayAccess on Doctrine\ORM\Mapping\JoinColumnMapping is deprecated

[KDederichs]

Describe the bug
We'll likely have a good while but I thought I'd open a ticket for it anyways:

It seems that array access on JoinColumnMapping has been deprecated and is now throwing warnings:

Using ArrayAccess on Doctrine\ORM\Mapping\JoinColumnMapping is deprecated and will not be possible in Doctrine ORM 4.0. Use the corresponding property instead. (ArrayAccessImplementation.php:18 called by CommonPreConfigurator.php:201, https://github.com/doctrine/orm/pull/11211, package doctrine/orm)

Using ArrayAccess on Doctrine\ORM\Mapping\JoinColumnMapping is deprecated and will not be possible in Doctrine ORM 4.0. Use the corresponding property instead. (ArrayAccessImplementation.php:18 called by EntityConfigurator.php:43, https://github.com/doctrine/orm/pull/11211, package doctrine/orm)

Probably easily fixable by checking if it's an array or JoinColumnMapping

To Reproduce
Use Easy Admin with ORM 3