Dockerfile: use COPY vs ADD; use of MAINTAINER is deprecated (codesandbox#150)

Author: robbyoconnor

Dockerfile.prod

@@ -1,8 +1,8 @@
 FROM node:8.2.1
-MAINTAINER Ives van Hoorne
+LABEL maintainer "Ives van Hoorne"
 
-ADD package.json /app/package.json
-ADD yarn.lock /app/yarn.lock
+COPY package.json /app/package.json
+COPY yarn.lock /app/yarn.lock
 
 WORKDIR /app
 RUN yarn install