Update api_version.py

Author: smubbs

shopify/api_version.py

@@ -33,7 +33,7 @@ def define_known_versions(cls):
                     if release == 'unstable':
                         cls.define_version(Unstable())
                     else:
-                        cls.define_version(Release(release)
+                        cls.define_version(Release(release))
 
     @classmethod
     def clear_defined_versions(cls):