Bump stripe-mock to 0.67.0

Author: ob-stripe

src/test/java/com/stripe/BaseStripeTest.java

@@ -32,7 +32,7 @@
 
 public class BaseStripeTest {
   // If changing this number, please also change it in `.travis.yml`.
-  private static final String MOCK_MINIMUM_VERSION = "0.66.0";
+  private static final String MOCK_MINIMUM_VERSION = "0.67.0";
 
   private static String port;