Add replace clause to composer.json for mnapoli package

[nstory]

Without this replace clause, it's possible to install both the mnapoli/php-di and php-di/php-di packages in the same project. Here is a sample composer.json which demonstrates this problem:

{
    "name": "nstory/tstprj",
    "require": {
      "php-di/php-di": "*",
      "mnapoli/php-di": "*"
    }
}

Running composer update with the above will create both vendor/mnapoli/php-di and vendor/php-di/php-di.

[mnapoli]

Nice idea, thank you!