build: Update gtk-doc dependency to 1.15
build: Update gtk-doc dependency to 1.15

Fixes: http://bugs.meego.com/show_bug.cgi?id=5714

GNOME/libsocialweb,ThomasBollmeier/libsocialweb-flickr-oauth,ThomasBollmeier/libsocialweb-flickr-oauth,GNOME/libsocialweb,ThomasBollmeier/libsocialweb-flickr-oauth,GNOME/libsocialweb,lcp/libsocialweb,lcp/libsocialweb,lcp/libsocialweb