Update versions

Author: mllemango

shopify/api_version.py

@@ -31,6 +31,8 @@ def define_known_versions(cls):
         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"))
 
     @classmethod
     def clear_defined_versions(cls):