PHP 7.2 compatibility
We use this extension in a big PHP 7.2 environment without problems. Sadly it is always a hassle to work around the composer restriction on the PHP version of this extension.
As long as there are no known limitiation due to PHP incompatibilities I'd suggest to only require a minimum PHP version and limit the maximum only to the major version (so that every 7.x version greater than the minimum is allowed). Then progressive users can just easily update their environment and test the extension for compatibility themselves. Conservative users will stay on older versions anyways. So there's no real reason to implment right restrictions on the PHP version.