knot-dns: 2.7.6 -> 2.8.0

https://gitlab.labs.nic.cz/knot/knot-dns/tags/v2.8.0
Some explanation for the patching is in this ML thread:
https://lists.nic.cz/pipermail/knot-dns-users/2019-March/001616.html

pkgs/servers/dns/knot-resolver/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, runCommand, pkgconfig, hexdump, which
+{ stdenv, fetchurl, fetchpatch, runCommand, pkgconfig, hexdump, which
 , knot-dns, luajit, libuv, lmdb, gnutls, nettle
 , cmocka, systemd, dns-root-data, makeWrapper
 , extraFeatures ? false /* catch-all if defaults aren't enough */
@@ -19,6 +19,14 @@ unwrapped = stdenv.mkDerivation rec {
     sha256 = "d1396888ec3a63f19dccdf2b7dbcb0d16a5d8642766824b47f4c21be90ce362b";
   };
 
+  patches = [
+    (fetchpatch {
+      name = "support-libzscanner-2.8.diff";
+      url = "https://gitlab.labs.nic.cz/knot/knot-resolver/commit/186f263.diff";
+      sha256 = "19zqigvc7m2a4j6bk9whx7gj0v009568rz5qwk052z7pzfikr8mk";
+    })
+  ];
+
   # Short-lived cross fix, as upstream is migrating to meson anyway.
   postPatch = ''
     substituteInPlace platform.mk --replace "objdump" "$OBJDUMP"