Use node 8.9.4

If you are getting errors about “The engine "node" is incompatible with 
this module. Expected version ">=8.9.4”.” after applying this change,
It means you need upgrade your node to 8.9.4. to do so:

if you use nvm: `nvm install` inside the canvas dir
If you use brew: `brew upgrade node`
If you use apt-get: see https://github.com/nodesource/distributions
If you use docker: rebuild your docker container

Closes: CORE-704

Test plan:
* js tests should pass
* webpack and brandable_css should generate the exact same
  CSS and JS output as before.
* all of our build tooling, including docker stuff, should continue
  to work and use Node 8. 

If you know of something else that needs to be updated to use node 8 
everywhere, let me know

Change-Id: Ic019710c219d8b8c627ce03e0dffde731cfa2856
Reviewed-on: https://gerrit.instructure.com/136802
Tested-by: Jenkins
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>

.nvmrc

@@ -1 +1 @@
-v6.9.5
+v8.9.4

Dockerfile-production

@@ -17,7 +17,7 @@ ENV DISABLE_V8_COMPILE_CACHE 1
 
 USER root
 WORKDIR /root
-RUN curl -sL https://deb.nodesource.com/setup_6.x | bash - \
+RUN curl -sL https://deb.nodesource.com/setup_8.x | bash - \
   && curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - \
   && echo "deb https://dl.yarnpkg.com/debian/ stable main" > /etc/apt/sources.list.d/yarn.list \
   && printf 'path-exclude /usr/share/doc/*\npath-exclude /usr/share/man/*' > /etc/dpkg/dpkg.cfg.d/01_nodoc \

build/Dockerfile.template

@@ -14,7 +14,7 @@ ENV DISABLE_V8_COMPILE_CACHE 1
 
 USER root
 WORKDIR /root
-RUN curl -sL https://deb.nodesource.com/setup_6.x | bash - \
+RUN curl -sL https://deb.nodesource.com/setup_8.x | bash - \
   && curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - \
   && echo "deb https://dl.yarnpkg.com/debian/ stable main" > /etc/apt/sources.list.d/yarn.list \
   && printf 'path-exclude /usr/share/doc/*\npath-exclude /usr/share/man/*' > /etc/dpkg/dpkg.cfg.d/01_nodoc \

docker-compose/phantomjs-karma/Dockerfile

@@ -8,7 +8,7 @@ RUN \
   apt-get update -yqq && \
   apt-get install -fyqq wget curl libfreetype6 libfontconfig
 
-RUN curl -sL https://deb.nodesource.com/setup_6.x | bash -
+RUN curl -sL https://deb.nodesource.com/setup_8.x | bash -
 RUN  apt-get update -qq \
   && apt-get install -qqy nodejs
 

package.json

@@ -3,7 +3,7 @@
   "license": "AGPL-3.0",
   "version": "0.0.0",
   "engines": {
-    "node": ">=6.9.5",
+    "node": ">=8.9.4",
     "yarn": "1.3.2"
   },
   "dependencies": {