[gtk-doc] ci: also add python3 as a direct dep

[Stefan Sauer <stefkost src gnome org>]

commit d2c526b380b904a9f9b0f90e77a31d0536732a9a
Author: Stefan Sauer <ensonic users sf net>
Date:   Fri Dec 14 08:55:53 2018 +0100

    ci: also add python3 as a direct dep

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 5bd98d8..8292c07 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -9,7 +9,7 @@ before_script:
   - 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-lxml python3-parameterized python3-pip
+                python3 python3-lxml python3-parameterized python3-pip
                 python3-pygments python3-unittest2
   - export LANG=C.UTF-8