Update slugs

[srajiang]

Summary

Soon we will introduce validation on front-matter content, specifically slugs before they can be published to Contentful.
We will accept slugs formatted with hyphens (-) only, no underscores(_) or other special characters.

This change fixes one such example in this repo

@wongjas Added you as a reviewer as an FYI!

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #1161 (b3adf35) into main (b696c72) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1161   +/-   ##
=======================================
  Coverage   71.71%   71.71%           
=======================================
  Files          15       15           
  Lines        1354     1354           
  Branches      402      402           
=======================================
  Hits          971      971           
  Misses        312      312           
  Partials       71       71           

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