[gnome-contacts] CI: fix build dir typo.

[Niels De Graef <nielsdg src gnome org>]

commit b8b7f98faf26e79270fce5a99833d26e30ac5d07
Author: Niels De Graef <nielsdegraef gmail com>
Date:   Sun Apr 8 10:39:12 2018 +0200

    CI: fix build dir typo.

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a4d9345..18e95a7 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -2,7 +2,7 @@
 .build_template: &distro_build
   script:
     - meson -Dmanpage=false _build
-    - ninja -C build install
+    - ninja -C _build install
 
 stages:
   - build-flatpak