Issue #55: Update Dockerfile to use multi-stage build

The Dockerfile now has two build stages, one for development with dependecies installed while
the production stage only has the application itself, making the production image much smaller.

Dockerfile

@@ -1,7 +1,4 @@
-FROM node:lts-alpine
-
-# install simple http server for serving static content
-RUN npm install -g http-server
+FROM node:lts-alpine as dev
 
 # make the 'app' folder the current working directory
 WORKDIR /app
@@ -19,4 +16,10 @@ COPY . .
 RUN npm run build
 
 EXPOSE 8080
-CMD [ "http-server", "dist" ]
+CMD [ "npm", "run", "dev" ]
+
+# production stage
+FROM nginx:stable-alpine as prod
+COPY --from=dev /app/dist /usr/share/nginx/html
+EXPOSE 80
+CMD ["nginx", "-g", "daemon off;"]