Docstring typo

[yaniccd]

Fixe ":math:``S_{2p}" in weingarten_circular_symplectic function docstring.

[nkar123412-hub]

I've fixed the missing backtick in the docstring of weingarten_circular_symplectic. The fix is available in my fork: https://github.com/nkar123412-hub/haarpy/tree/fix/docstring-typo

[yaniccd]

Fixed in PR #65.