Fix release date on the website.

This should also trigger a rebuild that will fix the bugged
`news/version_3.6.1.{es,fa}.html` pages.

wiki/src/inc/stable_amd64_date.html

-2018-03-17
\ No newline at end of file
+2018-03-18

wiki/src/news/version_3.6.1.mdwn

-[[!meta date="Sat, 17 Mar 2018 12:34:56 +0000"]]
+[[!meta date="Sun, 18 Mar 2018 18:30:11 +0100"]]
 [[!meta title="Tails 3.6.1 is out"]]
 [[!tag announce]]