Pin eslint-config-google version

The newest version of eslint-config-google introduced an eslint-rule
that was not conformant with the style used in Gerrit.

This change pins the version of eslint-config-google to the working
version 0.12.0, which is known to be working after change 213232 in the
Gerrit project.

Change-Id: Ia15ac6ac8f32ee0859496d7bc77a869184c83cb9
diff --git a/jenkins-docker/slave-node-wct/Dockerfile b/jenkins-docker/slave-node-wct/Dockerfile
index ab10ec6..1de2caa 100644
--- a/jenkins-docker/slave-node-wct/Dockerfile
+++ b/jenkins-docker/slave-node-wct/Dockerfile
@@ -11,5 +11,5 @@
 COPY wct.conf.json /home/jenkins/
 RUN chown jenkins:jenkins /home/jenkins/wct.conf.json
 
-RUN npm install --unsafe-perm -g eslint@"=4.19.0" eslint-config-google eslint-plugin-html typescript fried-twinkie@">0.2.0" polylint polymer-cli
+RUN npm install --unsafe-perm -g eslint@"=4.19.0" eslint-config-google@"=0.12.0" eslint-plugin-html typescript fried-twinkie@">0.2.0" polylint polymer-cli
 RUN npm install --unsafe-perm -g 'web-component-tester@$WCT_VER'