[gnome-books/wip/hadess/fix-ci] ci: Work-around evince build failure

[Bastien Nocera <hadess src gnome org>]

commit e96b33bfa6a0df137fe5cea0567fbd62481bcba5
Author: Bastien Nocera <hadess hadess net>
Date:   Sun Aug 25 11:23:10 2019 +0300

    ci: Work-around evince build failure
    
    evince failed to build/install the gtk-doc devhelp2 file, but we don't
    actually need the docs to run gnome-books.

 flatpak/org.gnome.Books.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/flatpak/org.gnome.Books.json b/flatpak/org.gnome.Books.json
index 59d70036..46ec24db 100644
--- a/flatpak/org.gnome.Books.json
+++ b/flatpak/org.gnome.Books.json
@@ -98,7 +98,7 @@
                              "-Dpreviewer=false", "-Ddbus=false",
                              "-Dbrowser_plugin=false", "-Dintrospection=true",
                              "-Dcomics=enabled", "-Dpdf=enabled",
-                             "-Dgspell=disabled" ],
+                             "-Dgspell=disabled", "-Dgtk_doc=false" ],
             "sources": [
                 {
                     "type": "git",