feat: Simplify dockerfile significantly

- Use docker library version of node
 - Assume dockerfile lives with sourcecode
 - Assume server can be started with `npm start` aka `node server.js`
 - Assumes all dependencies are listed in `package.json`

Dockerfile

@@ -1,13 +1,7 @@
-FROM debian:jessie
+# Pull base image.
+FROM node:0.10-onbuild
 
-RUN apt-get update
+# Node base will default the command to `node server.js`.
-RUN apt-get upgrade -yq
-RUN apt-get install -yq git nodejs-legacy npm
-RUN git clone https://github.com/benweet/stackedit.git
-
-WORKDIR stackedit
-RUN npm install
-RUN node_modules/bower/bin/bower install --allow-root --production --config.interactive=false
-CMD nodejs server.js
 
+# Expose port.
 EXPOSE 3000