Depend on mate-desktop 1.21.2 due to new gschema key

Author: lukefromdc

configure.ac

@@ -64,7 +64,7 @@ GTK_REQUIRED=3.22.0
 MARCO_REQUIRED=1.17.0
 MSD_REQUIRED=1.17.0
 MATEKBD_REQUIRED=1.17.0
-MATE_DESKTOP_REQUIRED=1.21.1
+MATE_DESKTOP_REQUIRED=1.21.2
 APPINDICATOR_REQUIRED=0.0.13
 
 ENGINES_FOLDER="theming-engines"