Bump Go to 1.8.4

Bumps the Go version used to 1.8.4, which contains security fixes;
https://groups.google.com/forum/#!topic/golang-announce/1hZYiemnkdE

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

libnetwork/Dockerfile.build

@@ -1,4 +1,4 @@
-FROM golang:1.8.3
+FROM golang:1.8.4
 RUN apt-get update && apt-get -y install iptables
 
 RUN go get github.com/tools/godep \