Update Dockerfile

Typo in original. Missing " * " on line 47.

Author: Justin Peter

articles/container-instances/container-instances-tutorial-prepare-app.md

@@ -44,7 +44,7 @@ The Dockerfile in the sample application shows how the container is built. It st
 ```Dockerfile
 FROM node:8.9.3-alpine
 RUN mkdir -p /usr/src/app
-COPY ./app/ /usr/src/app/
+COPY ./app/* /usr/src/app/
 WORKDIR /usr/src/app
 RUN npm install
 CMD node /usr/src/app/index.js