Magento 2.3 has removed its version information from the `composer.json` files since 2018-04-05

News
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1

https://github.com/magento/magento2/commit/95bfd2c7

Before

https://github.com/magento/magento2/blob/930d8801/composer.json#L1-L9

After

https://github.com/magento/magento2/blob/95bfd2c7/composer.json#L1-L8

2

I have updated my Magento version detection code for compatibility with Magento 2.3.