Replace Zend_Json with just a basic json_encode in the configurable product block view test

Author: dmanners

app/code/Magento/ConfigurableProduct/Test/Unit/Block/Product/View/Type/ConfigurableTest.php

@@ -200,7 +200,7 @@ public function testGetJsonConfig()
             ]);
 
         $expectedArray = $this->getExpectedArray($productId, $amount, $priceQty, $percentage);
-        $expectedJson = \Zend_Json::encode($expectedArray);
+        $expectedJson = json_encode($expectedArray);
 
         $this->jsonEncoder->expects($this->once())
             ->method('encode')