Update codes to have a consistancy

[baseplate-admin]

It seems that old syntax is used here :

1. pymdown-extensions/pymdownx/highlight.py

   Line 484 in 5dd162a

   super(HighlightTreeprocessor, self).__init__(md)

2. pymdown-extensions/pymdownx/highlight.py

   Line 542 in 5dd162a

   super(HighlightExtension, self).__init__(*args, **kwargs)

It should be changed to super().__init__(*args, *kwargs)

[facelessuser]

Sure. A PR is welcome.

[facelessuser]

#2218 modernizes super() usage