In composer.json you marked that this plugin supports php 7.0, but you used void as return type (ref: https://github.com/Neirda24/GuzzleBundleHeaderDisableCachePlugin/blob/master/src/EventListener/NoCacheSubscriber.php#L36) but this feature was introduced in php 7.1 (ref: https://wiki.php.net/rfc/void_return_type). You have two options:
- rise php version in composer.json to 7.1
- remove usage of all features introduced in php 7.1
In composer.json you marked that this plugin supports php 7.0, but you used
voidas return type (ref: https://github.com/Neirda24/GuzzleBundleHeaderDisableCachePlugin/blob/master/src/EventListener/NoCacheSubscriber.php#L36) but this feature was introduced in php 7.1 (ref: https://wiki.php.net/rfc/void_return_type). You have two options: