[Tails-dev] [review'n'merge] Few changes in Numerous_securit…

Hello, I mad few changes in Numerous_security_holes_in_3.12.mdwn:
- remove obsolete .po files
- change publication date, currently Numerous_security_holes_in_3.11
appear before Numerous_security_holes_in_3.12 in
https://tails.boum.org/security/index.en.html
- add a missing punctuation.
Please review and merge.

Repo: https://git-tails.immerda.ch/xin/tails/
Branch: Numerous_security_holes_in_3.12
Last Commit: 2bb390c0c4fbea0322d01a0f7c1bd80066f19ee5

Cheers.
xin