docs: update Markdown equation elements

[stdlib-bot]

This PR

• updates equation elements found in Markdown files

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
ml/base/loss/float64/squared-hinge-gradient	$\\color{green}208/208$ $\\color{green}+0.00\\%$	$\\color{green}14/14$ $\\color{green}+0.00\\%$	$\\color{green}2/2$ $\\color{green}+0.00\\%$	$\\color{green}208/208$ $\\color{green}+0.00\\%$

The above coverage report was generated for the changes in this PR.