package/shairport-sync: bump to version 2.4.2

Also add a hash file - github release tarballs are considered stable now.

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/shairport-sync/shairport-sync.hash

@@ -0,0 +1,2 @@
+# Locally calculated
+sha256  e3c70acc8a4516dfe0c77d7b0317c4a180cc722b22715b042ef8757d1a0e0f32  shairport-sync-2.4.2.tar.gz

package/shairport-sync/shairport-sync.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-SHAIRPORT_SYNC_VERSION = 2.4.1
+SHAIRPORT_SYNC_VERSION = 2.4.2
 SHAIRPORT_SYNC_SITE = $(call github,mikebrady,shairport-sync,$(SHAIRPORT_SYNC_VERSION))
 
 SHAIRPORT_SYNC_LICENSE = MIT, BSD-3c