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Records have been coming back from CloudFlare with garbage data. This change throws on invalid data now.

• Adds dig based resolver from the good folks at https://github.com/spatie/dns

• Suport SRV Record Data Types
• Update Code Style to PSR12

• Open up to symfony/event-dispatcher v5
• Deprecate support of PHP 7.1 and 7.2
• Update dev / main dependencies

If a TTL of 0 got returned for a record, the Cached resolver would set that as the TTL for the record set. It should instead default to the Cached::DEFAULT_TTL value.

Addresses a security vulnerability in require dev dependencies

• also brush up the README a little

Previously when cached records were returned, they were returned with the same TTL they were stored with, every time. This new method of retrieval accounts for the time passed between storage, retrieval, and the effect on the overall TTL of the record.

• Change internal call to symfony's event dispatcher based on version

• Address flaky integration test

• Cleanup tests for eventual PHPUnit 8 migration