[DRE-maint] Bug#902504: update jekyll to latest upstream release (blocks ruby-rouge update)

[Pander]

Package: jekyll
Version: 3.1.6+dfsg-3
Followup-For: Bug #902504

See also the update request at Ubuntu https://bugs.launchpad.net/ubuntu/+source/jekyll/+bug/1786230


-- System Information:
Debian Release: 9.4
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-6-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages jekyll depends on:
ii  ruby                        1:2.3.3
ii  ruby-classifier-reborn      2.0.4-1
ii  ruby-colorator              1.1.0-1
ii  ruby-jekyll-coffeescript    1.0.1-2
ii  ruby-jekyll-feed            0.3.1-1
ii  ruby-jekyll-gist            1.1.0-1
ii  ruby-jekyll-paginate        1.1.0-1
ii  ruby-jekyll-sass-converter  1.3.0-1
ii  ruby-jekyll-watch           1.3.0-1
ii  ruby-kramdown               1.12.0-1
ii  ruby-launchy-shim           2.3.0.1
ii  ruby-liquid                 3.0.6-1
ii  ruby-mercenary              0.3.5-1
ii  ruby-mime-types             2.6.1-1
ii  ruby-pygments.rb            0.6.3-2+deb9u1
ii  ruby-rdiscount              2.1.8-1+b3
ii  ruby-redcarpet              3.3.4-2
ii  ruby-rouge                  2.0.2-1
ii  ruby-safe-yaml              1.0.4-1
ii  ruby-toml                   0.1.2-4
ii  xdg-utils                   1.1.1-1+deb9u1

Versions of packages jekyll recommends:
pn  ruby-mysql      <none>
pn  ruby-sequel     <none>
pn  ruby-sequel-pg  <none>

jekyll suggests no packages.

-- no debconf information