Improve unit test to not rely on mongodb server version dependent message

tests/Alcaeus/MongoDbAdapter/Mongo/MongoClientTest.php

@@ -74,7 +74,7 @@ class MongoClientTest extends TestCase
     public function testGetHostsExceptionHandling()
     {
         $this->expectException(\MongoConnectionException::class);
-        $this->expectExceptionMessageRegExp('/No suitable servers found/');
+        $this->expectExceptionMessageRegExp('/fake_host/');
 
         $client = $this->getClient(null, 'mongodb://fake_host');
         $client->getHosts();