set docker cert path

.drone.star

@@ -99,7 +99,7 @@ def buildContainer(PHP_VERSION, ALPINE_VERSION, TESTING_REPO, PHP_SESSION):
           }
         ],
         'environment': {
-          'DOCKER_TLS_CERTDIR': '/certs',
+          'DOCKER_CERT_PATH': '/certs',
           'DOCKER_HOST': 'tcp://docker:2376',
           'DOCKER_TLS_VERIFY': '1'
         },