devtools: bump to Go 1.15.5

Change-Id: Ib6d60478a49776c719ab3f05aa43c497be82d5f2
diff --git a/devtools/kube/hackdoc.libsonnet b/devtools/kube/hackdoc.libsonnet
index d849ebb..cb1c319 100644
--- a/devtools/kube/hackdoc.libsonnet
+++ b/devtools/kube/hackdoc.libsonnet
@@ -3,7 +3,7 @@
 
 {
     cfg:: {
-        image: "registry.k0.hswaw.net/q3k/hackdoc:1600885335-2b8f3c4af735f193604ee2f9240e063071a62de6",
+        image: "registry.k0.hswaw.net/q3k/hackdoc:1606469587-42b21ecd84b713faf1c65c4ddceb74f559fe94bd",
         publicFQDN: error "public FQDN must be set",
     },