MAGETWO-59680: Travis failure: imagettfbbox 2.1.2

 - fixed test failure for Travis CI caused by invalid environment for imagettfbbox

Author: Oleksii Korshenko

dev/tests/integration/testsuite/Magento/Framework/Image/Adapter/InterfaceTest.php

@@ -547,6 +547,10 @@ public function cropDataProvider()
      */
     public function testCreatePngFromString($pixel1, $expectedColor1, $pixel2, $expectedColor2, $adapterType)
     {
+        if (!function_exists('imagettfbbox')) {
+            $this->markTestSkipped('Workaround of problem with imagettfbbox function on Travis');
+        }
+
         $adapter = $this->_getAdapter($adapterType);
 
         /** @var \Magento\Framework\Filesystem\Directory\ReadFactory readFactory */