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
math/base/special/expf	$\\color{red}494/496$ $\\color{green}+99.60\\%$	$\\color{red}23/24$ $\\color{green}+95.83\\%$	$\\color{green}4/4$ $\\color{green}+100.00\\%$	$\\color{red}494/496$ $\\color{green}+99.60\\%$
ml/base/loss/float64/hinge-gradient	$\\color{green}206/206$ $\\color{green}+100.00\\%$	$\\color{green}14/14$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}206/206$ $\\color{green}+100.00\\%$
ml/base/loss/float64/huber-gradient	$\\color{green}202/202$ $\\color{green}+100.00\\%$	$\\color{green}12/12$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}202/202$ $\\color{green}+100.00\\%$
ml/base/loss/float64/log-gradient	$\\color{green}197/197$ $\\color{green}+100.00\\%$	$\\color{green}11/11$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}197/197$ $\\color{green}+100.00\\%$
stats/base/dists/wald/mgf	$\\color{green}314/314$ $\\color{green}+100.00\\%$	$\\color{green}23/23$ $\\color{green}+100.00\\%$	$\\color{green}4/4$ $\\color{green}+100.00\\%$	$\\color{green}314/314$ $\\color{green}+100.00\\%$

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