Remove "Psr" prefix from spec base tests.

Author: makasim

Tests/Spec/NullMessageTest.php

@@ -3,9 +3,9 @@
 namespace Enqueue\Null\Tests\Spec;
 
 use Enqueue\Null\NullMessage;
-use Interop\Queue\Spec\PsrMessageSpec;
+use Interop\Queue\Spec\MessageSpec;
 
-class NullMessageTest extends PsrMessageSpec
+class NullMessageTest extends MessageSpec
 {
     /**
      * {@inheritdoc}