Add node-4 dockerfile to debug

.dockerignore

+.idea
+.save
+logs
+*.log
+npm-debug.log*
+build/Release
+node_modules
+.tern-port
+dist/steem-tests.min.js*
+.tern-port
+.envrc
+dist

node-4.dockerfile

+FROM node:4
+ADD ./package.json /steemjs/package.json
+WORKDIR /steemjs
+RUN npm install
+ADD . /steemjs
+RUN npm test