Use constant for updated_at column name (#108)

src/Drivers/DatabaseDriver.php

@@ -278,7 +278,7 @@ public function set($feature, $scope, $value): void
             'value' => json_encode($value, flags: JSON_THROW_ON_ERROR),
             static::CREATED_AT => $now = Carbon::now(),
             static::UPDATED_AT => $now,
-        ], uniqueBy: ['name', 'scope'], update: ['value', 'updated_at']);
+        ], uniqueBy: ['name', 'scope'], update: ['value', static::CREATED_AT]);
     }
 
     /**