Update SimpleCacheAdapter.php (#60)

When using `SimpleCacheAdapter` with the Laravel Redis cache adapter, the method `getIdWithHash` tries to return the string representation of the value in the store directly. Giving the following exception ```Symfony\Component\Debug\Exception\FatalThrowableError with message 'Return value of FlixTech\SchemaRegistryApi\Registry\Cache\SimpleCacheAdapter::getIdWithHash() must be of the type int or null, string returned'```

Co-authored-by: Thomas Ploch <profiploch@gmail.com>

Author: danlitman

src/Registry/Cache/SimpleCacheAdapter.php

@@ -76,8 +76,13 @@ public function getWithId(int $schemaId): ?AvroSchema
      */
     public function getIdWithHash(string $hash): ?int
     {
-
-        return $this->cache->get($hash);
+        $rawId = $this->cache->get($hash);
+        
+        if (null === $rawId) {
+            return null;
+        }
+        
+        return (int) $rawId;
     }
 
     /**