[gtk-doc] ci: add more direct deps

[Stefan Sauer <stefkost src gnome org>]

commit f28adca8b68ed0887d9c2819847644c964a4d08e
Author: Stefan Sauer <ensonic users sf net>
Date:   Fri Dec 14 09:25:16 2018 +0100

    ci: add more direct deps

 .gitlab-ci.yml | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 8292c07..7334975 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -8,9 +8,10 @@ before_script:
   - apt update -qq
   - apt install -y -qq --no-install-recommends
                 autoconf automake build-essential libtool make meson pkg-config
-                docbook docbook-xsl libxml2-utils xsltproc libglib2.0-dev
-                python3 python3-lxml python3-parameterized python3-pip
-                python3-pygments python3-unittest2
+                docbook docbook-xml docbook-xsl libxml2-utils xsltproc
+                libglib2.0-dev
+                python3 python3-dev python3-lxml python3-parameterized
+                python3-pip python3-pygments python3-unittest2
   - export LANG=C.UTF-8
 
 stages: