[gnome-software] trivial: Fix installing the gtk-doc files when using meson

[Richard Hughes <rhughes src gnome org>]

commit b59ec607dbe3afb5795274e5713a7879fac37466
Author: Richard Hughes <richard hughsie com>
Date:   Mon Apr 10 13:16:44 2017 +0100

    trivial: Fix installing the gtk-doc files when using meson

 doc/api/meson.build |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/doc/api/meson.build b/doc/api/meson.build
index 5a51e64..aa8f873 100644
--- a/doc/api/meson.build
+++ b/doc/api/meson.build
@@ -1,5 +1,6 @@
-gnome.gtkdoc('gnome-software',
-  src_dir : join_paths(meson.source_root(), 'src'),
+gnome.gtkdoc(
+  'gnome-software',
+  src_dir : join_paths(meson.source_root(), 'lib'),
   main_xml : 'gnome-software-docs.xml',
   html_assets : [
     'gs-example-details.png',