update to phpunit8

Structural/DataMapper/Tests/DataMapperTest.php

@@ -20,11 +20,10 @@ class DataMapperTest extends TestCase
         $this->assertInstanceOf(User::class, $user);
     }
 
-    /**
-     * @expectedException \InvalidArgumentException
-     */
     public function testWillNotMapInvalidData()
     {
+        $this->expectException(\InvalidArgumentException::class);
+
         $storage = new StorageAdapter([]);
         $mapper = new UserMapper($storage);