fix permalink: /specification-refence → /specification-reference

[chocolateboy]

currently the typo link works and the correct link 404s e.g.:

• http://guides.rubygems.org/specification-reference 404
• http://guides.rubygems.org/specification-refence OK

see #205

[bundlerbot]

☔ The latest upstream changes (presumably #207) made this pull request unmergeable. Please resolve the merge conflicts.

[colby-swandale]

Thanks for the PR. I'm cautious to accept this PR as this would break the URLs that are indexed on Google. We should try to make the page accessible via /specification-refence and also /specification-reference

[olleolleolle]

@chocolateboy I wonder - for me, currently, the first link is OK and the second link is 404.

Does this change things about this PR?

[chocolateboy]

@olleolleolle The typo's still there. The correct link only started working again (and the incorrect link only stopped working) after #207.

[chocolateboy]

Incidentally, #207 says:

PR #201 appears to have broken the links that Google has indexed.

I think the Google indexing thing is a red herring. Google was pointing to /specification-reference when I raised #205, and is still pointing to it now:

And I can't find any references to specification-refence in its cache: