PolyGerrit: Install eslint and polylint

Per google group
https://groups.google.com/forum/#!topic/repo-discuss/Fw92k-6MZrU

also installing polylint so we doint have to do it later when
https://gerrit-review.googlesource.com/#/c/107135/ is merge

Change-Id: Ic6ec5bdfbf1f9eb1640a1a4486e90d0f3577d2cc
diff --git a/jenkins-docker/slave/Dockerfile b/jenkins-docker/slave/Dockerfile
index 7302db7..3249aa0 100644
--- a/jenkins-docker/slave/Dockerfile
+++ b/jenkins-docker/slave/Dockerfile
@@ -52,7 +52,7 @@
 
 # PolyGerrit tests
 
-RUN npm install -g web-component-tester
+RUN npm install -g web-component-tester eslint eslint-config-google eslint-plugin-html polylint
 RUN curl -sL https://dl-ssl.google.com/linux/linux_signing_key.pub | apt-key add -
 RUN sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list'
 RUN apt-get update && apt-get install -y google-chrome-stable