[gexiv2] ci: Add gtk-doc

[Jens Georg <jensgeorg src gnome org>]

commit 6ed63b8728edb3f377a8a6f76d06ec0ab423b495
Author: Jens Georg <mail jensge org>
Date:   Sun Nov 18 12:17:57 2018 +0100

    ci: Add gtk-doc

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 0807e67..c31f714 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -4,7 +4,7 @@ before_script:
   - dnf update -y --nogpgcheck
   - dnf install -y --nogpgcheck meson gcc-c++ exiv2-devel gobject-introspection-devel
                                 ninja-build python2-devel python2-gobject-base vala
-                                python3-devel python3-gobject-base
+                                python3-devel python3-gobject-base gtk-doc
   - export LANG=C.UTF-8
 
 stages: