UPGRADE FROM 2.1 to 2.2
=======================

* Deprecated using doctrine/cache for metadata caching. The `setCacheDriver` and
  `getCacheDriver` methods in `Doctrine\Persistence\Mapping\AbstractMetadata`
  have been deprecated. Please use `getCache` and `setCache` with a PSR-6 
  implementation instead. Note that even after switching to PSR-6,
  `getCacheDriver` will return a cache instance that wraps the PSR-6 cache.
  Note that if you use a custom implementation of doctrine/cache, the library
  may not be able to provide a forward compatibility layer. The cache
  implementation MUST extend the `Doctrine\Common\Cache\CacheProvider` class.