abuild: force pkgrel in APKBUILD

its needed for bumping pkgrel with sed and similar

abuild.in

@@ -91,7 +91,7 @@ sanitycheck() {
 		$APK version --check -q "$pkgver" ||\
 			die "$pkgver is not a valid version"
 	fi
-	[ -z "$pkgrel" ] && warning "Missing pkgrel in APKBUILD. Using pkgrel=0"
+	[ -z "$pkgrel" ] && die "Missing pkgrel in APKBUILD"
 	[ -z "$pkgdesc" ] && die "Missing pkgdesc in APKBUILD"
 	[ -z "$url" ] && die "Missing url in APKBUILD"
 	[ -z "$license" ] && die "Missing license in APKBULID"