debian: depend on gawk

qubes.GetAppmenus uses "nextfile" which is gawk-specific.

Fixes qubesos/qubes-issues#1062

debian/control

@@ -13,6 +13,7 @@ Depends:
     dmsetup,
     ethtool,
     fakeroot,
+    gawk,
     imagemagick,
     init-system-helpers,
     initscripts,