build: update lightning-onion commit hash

In this commit, we update the version of lightning-onion that we pin
against to point to a version that has recently had a nil pointer panic
bug fix.

Gopkg.lock

@@ -154,7 +154,7 @@
 [[projects]]
   name = "github.com/lightningnetwork/lightning-onion"
   packages = ["."]
-  revision = "6d4b1353e2835def84ee240f40499464521c6046"
+  revision = "c86137582e53fe3ba26681a98f911b546970893e"
 
 [[projects]]
   name = "github.com/ltcsuite/ltcd"
@@ -359,6 +359,6 @@
 [solve-meta]
   analyzer-name = "dep"
   analyzer-version = 1
-  inputs-digest = "def340dd46b9ae439bf7c1e27155358aba5bb709c613fc1c577dacc4a2d4a1be"
+  inputs-digest = "0e386a2f0dff9303b03047f7499411379163ed3ca2b4a65161742e1b0fa23ec8"
   solver-name = "gps-cdcl"
   solver-version = 1

Gopkg.toml

@@ -44,7 +44,7 @@
 
 [[constraint]]
   name = "github.com/lightningnetwork/lightning-onion"
-  revision = "6d4b1353e2835def84ee240f40499464521c6046"
+  revision = "c86137582e53fe3ba26681a98f911b546970893e"
 
 [[constraint]]
   name = "github.com/ltcsuite/ltcd"