Fix #140: camel_to_snake adds underscore after digits

Fixed regex to add underscore between digit sequences and uppercase letters.
Example: camel_to_snake('python2Thing') now returns 'python2_thing'
instead of 'python2thing'.

Author: BLACKBEARDSOUL

src/graphql/pyutils/convert_case.py

@@ -6,7 +6,7 @@
 
 __all__ = ["camel_to_snake", "snake_to_camel"]
 
-_re_camel_to_snake = re.compile(r"([a-z]|[A-Z0-9]+)(?=[A-Z])")
+_re_camel_to_snake = re.compile(r"([a-z]|[A-Z0-9]+(?=[A-Z])|[0-9]+)(?=[A-Z])")
 _re_snake_to_camel = re.compile(r"(_)([a-z\d])")