[gtk-doc] ci: workaround broken python packages

[Stefan Sauer <stefkost src gnome org>]

commit eab70b1b7eb1ce5c8a7b5f8d9ac865f88c98d321
Author: Stefan Sauer <ensonic users sf net>
Date:   Fri Dec 14 20:57:26 2018 +0100

    ci: workaround broken python packages
    
    pip3 should probably install setuptools if it needs it.

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 9ae7b53..9704337 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -7,7 +7,7 @@ before_script:
                 dblatex docbook docbook-xml docbook-xsl libxml2-utils xsltproc
                 libglib2.0-dev
                 python3 python3-dev python3-lxml python3-parameterized
-                python3-pip python3-pygments python3-unittest2
+                python3-pip python3-pygments python3-setuptools python3-unittest2
   - pip3 install anytree
   - export LANG=C.UTF-8