Skip YAML tests as the extension is not on Travis :(

Author: repejota

test/YAMLEncoderTest.php

@@ -40,6 +40,10 @@ public function setUp()
      */
     public function testRequestArray()
     {
+        $this->markTestSkipped(
+            'The YAML extension is not available.'
+        );
+
         $this->c->subscribe(
             'sayhello',
             function ($res) {