add support for more recent nomad version

docker/Dockerfile

@@ -1,5 +1,5 @@
-FROM golang:1.8.0-alpine
-ARG NOMAD_VERSION=0.5.5
+FROM golang:1.10.3-alpine
+ARG NOMAD_VERSION=0.8.4
 COPY context /context
 RUN apk add --no-cache tar make git gcc musl-dev zip tree bash
 WORKDIR $GOPATH/src/github.com/hashicorp/
@@ -8,8 +8,8 @@ WORKDIR nomad
 RUN git fetch
 RUN git checkout v${NOMAD_VERSION} &&\
   make bootstrap &&\
-  make bin &&\
-  cp $GOPATH/bin/nomad /context/
+  make pkg/linux_amd64/nomad &&\
+  cp pkg/linux_amd64/nomad /context/
 WORKDIR /context
 USER nobody
 CMD ["tar", "cz", "."]