Fix relative link in PR Template

[joshbruce]

Description

PR fixes relative link issue to RELEASE.md in PR template.

Review

Submitter

• All tests pass (CI should take care of this, once in place).
• All lint checks pass (CI should take care of this, once in place).
• Tests
  • Test(s) exist to ensure functionality works (if no new tests added, list which tests cover this functionality).
  • No tests required for this PR.
• Is release:
  • Version in package.json has been updated (see RELEASE.md).
  • The marked.min.js has been updated; or,
  • release does not change library.

Reviewer

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