Release process: fix typo.

No idea this can possibly have worked recently.

wiki/src/contribute/release_process.mdwn

@@ -1002,7 +1002,7 @@ and on the live wiki (even for a release candidate):
        | ssh bittorrent.lizard gpg --import
     scp \
        "${ISOS:?}/tails-amd64-${VERSION:?}.torrent" \
-       "${ISOS_PATH:?}.sig" \
+       "${ISO_PATH:?}.sig" \
        bittorrent.lizard: && \
     ssh bittorrent.lizard << EOF
        mkdir --mode 0755 "tails-amd64-${VERSION:?}" && \