build: update to latest neutrino commit

In this commit, we update to the latest version of neutrino. This
version has an important bug fixes which fixes an issue where we
wouldn't detect a duplicate incoming cfheader message, and panic due to
trying to write the same header twice.

Gopkg.lock

@@ -268,7 +268,7 @@
   revision = "462a8a75388506b68f76661af8d649f0b88e5301"
 
 [[projects]]
-  digest = "1:6b3292ab3b4b5636b1bf10aad46c9377ea84316e662db00edcd4fc763592c2f2"
+  digest = "1:9d36cf09ab96eba14b70775f1284fa9741a212d2b49c08750b7112f9545a807b"
   name = "github.com/lightninglabs/neutrino"
   packages = [
     ".",
@@ -279,7 +279,7 @@
     "headerlist",
   ]
   pruneopts = "UT"
-  revision = "8018ab76e70acd3a56bc3857a80743f0ed1c86ce"
+  revision = "9a42f7df21be82a69f04caa83bce4034dca72764"
 
 [[projects]]
   digest = "1:58ab6d6525898cbeb86dc29a68f8e9bfe95254b9032134eb9458779574872260"

Gopkg.toml

@@ -44,7 +44,7 @@
 
 [[constraint]]
   name = "github.com/lightninglabs/neutrino"
-  revision = "8018ab76e70acd3a56bc3857a80743f0ed1c86ce"
+  revision = "9a42f7df21be82a69f04caa83bce4034dca72764"
 
 [[constraint]]
   name = "github.com/lightningnetwork/lightning-onion"