* Makefile.in (appdatadir): Use the non-obsolete location "metainfo".

* Makefile.in (appdatadir): Use the non-obsolete location "metainfo".

; https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html
; "AppStream tools scan the /usr/share/appdata/ path for legacy
; compatibility as well.  It should not be used anymore by new
; software though, even on older Linux distributions (like RHEL 7
; and Ubuntu 16.04 LTS) the metainfo path is well supported.  Support
; for the legacy path might be dropped completely in future."