USWDS-Site - HTMLProofer: Update 18f method links

[mahoneycm]

Summary

Update broken and redirect links flagged by HTMLProofer.

One of the 18f method links did not properly redirect to new path and caused a proofing error. I updated the other links which properly redirected for consistency.

Also updated showcase link that was causing an occasional 301 error.

Related issue

Closes #2720

Preview link

• Showcase page →
  • Methods card link
  • USGS Publications Warehouse link
  • Federal Public Key Infrastructure Guides link
• Sample contract language page →
  • 18f Methods link
  • User scenarios link
• Accessibility guidance page →
  • 18F’s collection of human-centered design tools link
• Design principles page →
  • 18F methods link
  • Prototypes link
  • 18F's human-centered design methods link
  • Interview checklist link
  • The Journey Mapping method link
• Research page →
  • 18F Methods link
  • User interviews link
  • Card sorting link
  • Usability testing link
• Blog post: Improving emergency response
  • Affinity map link

Problem statement

The interview checklist link on the Design Principles brings users to a 404 page.

Occasional HTMLProofer errors caused by redirects.

Solution

• Update Interview checklist link to match new 18f guide url path
• Update other 18f method links to match the new pattern
• Update PUBS link to match redirect

Major changes

N/A

Testing and review

1. Confirm no HTMLProofer errors are found
2. Confirm each of the updated links brings users to the appropriate pages without error
3. Confirm link text is appropriate
4. Confirm there are no additional instances of methods.18f.gov

[annepetersen]

Keeping a light eye here: could someone check the CircleCI fails here and let me know if this is good to merge so we can also then merge #2716?

[mahoneycm]

@amyleadem Updated the relevant link in b391347!