Add redirects for old docs locations

[JimMadge]

Closes #979

This adds two redirects, which I hope in combination will solve the issue.

• The first handles the old locations of translations https://allcontributors.org/docs/<lang>/abc -> https://allcontributors.org/docs/abc
• The second handles the docs previously being severed at the /docs/ path, https://allconttributors.org/docs/abc -> https://allcontributors.org/abc

So, I hope this should fix the cases where,

• There is an old link to a docs page in a particular language
• There is an old link which didn't specify a language and let the browser/web server choose.

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[JimMadge]

Seems to work on the preview,

• https://deploy-preview-983.staging.allcontributors.org/docs/en/emoji-key
• https://deploy-preview-983.staging.allcontributors.org/docs/emoji-key