Update 2021-07 version

Author: mllemango

shopify/api_version.py

@@ -27,12 +27,12 @@ def define_version(cls, version):
     @classmethod
     def define_known_versions(cls):
         cls.define_version(Unstable())
-        cls.define_version(Release("2020-01"))
         cls.define_version(Release("2020-04"))
         cls.define_version(Release("2020-07"))
         cls.define_version(Release("2020-10"))
         cls.define_version(Release("2021-01"))
         cls.define_version(Release("2021-04"))
+        cls.define_version(Release("2021-07"))
 
     @classmethod
     def clear_defined_versions(cls):