Update NodeJS to 4.x

Fixes memory leak caused by nodejs/node#1309

.travis.yml

@@ -1,6 +1,6 @@
 language: node_js
 node_js:
-  - "0.12"
+  - "4.1"
 
 install:
   - npm config set cache ./node_modules_cache

Dockerfile

@@ -28,7 +28,7 @@ RUN echo "Disabling non-essential packages" && \
     echo "Adding nodejs gpg key" && \
     curl -sL https://deb.nodesource.com/gpgkey/nodesource.gpg.key | apt-key add - && \
     echo "Adding nodejs repo" && \
-    echo 'deb https://deb.nodesource.com/node jessie main' > /etc/apt/sources.list.d/nodesource.list && \
+    echo 'deb https://deb.nodesource.com/node_4.x jessie main' > /etc/apt/sources.list.d/nodesource.list && \
     echo "Installing required packages" && \
     apt-get -qq update && \
     apt-get -qq install \