Use node 4 for travis and docker

.travis.yml

@@ -1,6 +1,6 @@
 language: node_js
 node_js:
-  - "5"
+  - "4"
 env:
   - CXX=g++-4.8
 addons:

Dockerfile

@@ -7,7 +7,7 @@ RUN apt-get -qq update \
     build-essential \
     python \
     xvfb \
-&& curl -sL https://deb.nodesource.com/setup_5.x | bash - \
+&& curl -sL https://deb.nodesource.com/setup_4.x | bash - \
 && apt-get -y install nodejs \
 && apt-get clean