mockgun: update highest pickle protocol for py3.7

Author: Mathieu

shotgun_api3/lib/mockgun/schema.py

@@ -84,9 +84,8 @@ def _read_file(cls, path):
             return pickle.load(fh)
 
 
-# Highest protocol that Python 2.4 supports, which is the earliest version of Python we support.
-# Actually, this is the same version that Python 2.7 supports at the moment!
-_HIGHEST_24_PICKLE_PROTOCOL = 2
+# Highest protocol that Python 3.7 supports, which is the earliest version of Python we support.
+_HIGHEST_37_PICKLE_PROTOCOL = 4
 
 
 # ----------------------------------------------------------------------------
@@ -108,13 +107,13 @@ def generate_schema(shotgun, schema_file_path, schema_entity_file_path):
     schema = shotgun.schema_read()
     fh = open(schema_file_path, "wb")
     try:
-        pickle.dump(schema, fh, protocol=_HIGHEST_24_PICKLE_PROTOCOL)
+        pickle.dump(schema, fh, protocol=_HIGHEST_37_PICKLE_PROTOCOL)
     finally:
         fh.close()
 
     schema_entity = shotgun.schema_entity_read()
     fh = open(schema_entity_file_path, "wb")
     try:
-        pickle.dump(schema_entity, fh, protocol=_HIGHEST_24_PICKLE_PROTOCOL)
+        pickle.dump(schema_entity, fh, protocol=_HIGHEST_37_PICKLE_PROTOCOL)
     finally:
         fh.close()