docs: fix broken Markdown link (issue #11868)

[bhumikasudarshani-cmd]

Fixes a broken Markdown link in lib/node_modules/@stdlib/datasets/cmudict/README.md.

The original URL (http://www.speech.cs.cmu.edu/cgi-bin/cmudict#about) is no longer
accessible (HTTP status 0). Updated to the current official GitHub repositor

Related Issues
resolves #11868

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Coverage Report

Package	Statements	Branches	Functions	Lines
blas/base/dgemv	$\color{red}748/749$ $\color{green}+99.87%$	$\color{red}116/117$ $\color{green}+99.15%$	$\color{green}6/6$ $\color{green}+100.00%$	$\color{red}748/749$ $\color{green}+99.87%$
datasets/cmudict	$\color{green}333/333$ $\color{green}+100.00%$	$\color{green}34/34$ $\color{green}+100.00%$	$\color{green}3/3$ $\color{green}+100.00%$	$\color{green}333/333$ $\color{green}+100.00%$
ndarray/base/unary-by	$\color{red}5062/11150$ $\color{green}+45.40%$	$\color{green}44/44$ $\color{green}+100.00%$	$\color{red}0/43$ $\color{green}+0.00%$	$\color{red}5062/11150$ $\color{green}+45.40%$

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