Update version and date for 3.7.

wiki/src/inc/stable_amd64_date.html

-2018-04-03
\ No newline at end of file
+2018-05-09
\ No newline at end of file

wiki/src/inc/stable_amd64_gpg_verify.html

-gpg --no-options --keyid-format 0xlong --verify tails-amd64-3.6.2.iso.sig tails-amd64-3.6.2.iso
+gpg --no-options --keyid-format 0xlong --verify tails-amd64-3.7.iso.sig tails-amd64-3.7.iso

wiki/src/inc/stable_amd64_iso_sig_url.html

-https://tails.boum.org/torrents/files/tails-amd64-3.6.2.iso.sig
+https://tails.boum.org/torrents/files/tails-amd64-3.7.iso.sig

wiki/src/inc/stable_amd64_iso_url.html

-http://dl.amnesia.boum.org/tails/stable/tails-amd64-3.6.2/tails-amd64-3.6.2.iso
+http://dl.amnesia.boum.org/tails/stable/tails-amd64-3.7/tails-amd64-3.7.iso

wiki/src/inc/stable_amd64_torrent_url.html

-https://tails.boum.org/torrents/files/tails-amd64-3.6.2.torrent
+https://tails.boum.org/torrents/files/tails-amd64-3.7.torrent

wiki/src/inc/stable_amd64_version.html

-3.6.2
+3.7