docs: sort the file list in the schemas Makefile

docs/schemas/Makefile.am

@@ -2,16 +2,16 @@
 
 schemadir = $(pkgdatadir)/schemas
 schema_DATA = \
+	capability.rng \
 	domain.rng \
 	domainsnapshot.rng \
 	interface.rng \
 	network.rng \
+	nodedev.rng \
+	nwfilter.rng \
 	secret.rng \
 	storageencryption.rng \
 	storagepool.rng \
-	storagevol.rng \
-	nodedev.rng \
-	capability.rng \
-	nwfilter.rng
+	storagevol.rng
 
 EXTRA_DIST = $(schema_DATA)