Added support for Azure Web Apps On Linux

Dockerfile

@@ -1,4 +1,4 @@
-FROM node
+FROM node:6.11-alpine
 
 # Create app directory
 RUN mkdir -p /usr/src/app
@@ -12,4 +12,4 @@ RUN npm install
 # Bundle app source
 COPY . /usr/src/app
 
-CMD [ "npm", "start" ]
+CMD [ "npm", "start" ]