Upgrade Docker image to node 8/npm5.

.taskcluster.yml

@@ -15,7 +15,7 @@ tasks:
     workerType: "{{ taskcluster.docker.workerType }}"
     payload:
       maxRunTime: 1200
-      image: "standard8/one-off-system-add-ons.2017030801.800ba54a4bd5"
+      image: "standard8/one-off-system-add-ons:2017081801.a6a1f5c1d971"
       command:
         - "/bin/bash"
         - "-lc"

docker-lint/Dockerfile

@@ -3,3 +3,6 @@ FROM quay.io/mozilla/lint
 
 # Add git to the image.
 RUN apt-get update -y && apt-get install -y git
+
+ADD install-node.sh /build/install-node.sh
+RUN bash /build/install-node.sh

docker-lint/install-node.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# This script installs Node v8.
+
+wget https://nodejs.org/dist/v8.4.0/node-v8.4.0-linux-x64.tar.gz
+echo 'd12bf2389a6b57341528a33de62561edd7ef25c23fbf258d48758fbe3d1d8578  node-v8.4.0-linux-x64.tar.gz' | sha256sum -c
+tar -C /usr/local -xz --strip-components 1 < node-v8.4.0-linux-x64.tar.gz
+node -v  # verify
+npm -v