Replace 'npm install' with 'yarn install'

Dockerfile

@@ -9,6 +9,10 @@ ENV HOME /root
 # When Ubuntu has nginx >= 1.11.0 we can switch back.
 RUN  add-apt-repository ppa:nginx/development
 
+# Add Yarn repository
+RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
+RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
+
 # Install system packages
 RUN apt-get update && apt-get upgrade -y # 22FEB2017
 RUN apt-get install -y \
@@ -42,7 +46,8 @@ RUN apt-get install -y \
      python-dbg        \
      python-dev        \
      python-pip        \
-     python-virtualenv
+     python-virtualenv \
+     yarn
 
 # Install python dependencies
 ADD requirements.txt requirements.txt
@@ -84,7 +89,7 @@ ADD package.json package.json
 ADD tsconfig.json tsconfig.json
 ADD webpack.config.js webpack.config.js
 ADD typings.json typings.json
-RUN npm install
+RUN yarn install --ignore-engines
 RUN npm link typescript
 
 # Add static files