l10n: updated Icelandic (is)
l10n: updated Icelandic (is)

contributors:
  Oktavia
  Sveinn í Felli

updated from:
  repo: https://github.com/freedomofpress/securedrop-i18n
  revision: 75d090c303ed9827cb5fd0eb647f322b56d5d707

conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop