move appdata to metainfo directory

fixes #280

Author: monsta

data/Makefile.am

@@ -4,7 +4,7 @@ desktop_DATA 	 = $(desktop_in_files:.desktop.in=.desktop)
 @INTLTOOL_DESKTOP_RULE@
 
 @INTLTOOL_XML_RULE@
-appdatadir = $(datadir)/appdata
+appdatadir = $(datadir)/metainfo
 appdata_in_files = pluma.appdata.xml.in
 appdata_DATA = $(appdata_in_files:.xml.in=.xml)