Added docker file and use yarn

.dockerignore

+.git
+node_modules
+build

Dockerfile

+# stage: 1
+FROM node:11 as react-build
+WORKDIR /app
+COPY . ./
+RUN yarn
+ENV SASS_PATH=/app/node_modules
+RUN yarn build
+# stage: 2 - production container image
+FROM nginx:alpine
+COPY --from=react-build /app/build /usr/share/nginx/html
+EXPOSE 80
+CMD ["nginx", "-g", "daemon off;"]