ci: do things within a new directory

Dockerfile

 FROM node:12
 
+ENV HOME "/home/pubsweet"
+RUN mkdir -p ${HOME}
+WORKDIR ${HOME}
+
 # Install chrome and firefox
 RUN curl -sL http://dl-ssl.google.com/linux/linux_signing_key.pub | apt-key add -
 RUN echo 'deb http://dl.google.com/linux/chrome/deb/ stable main' >> /etc/apt/sources.list.d/google.list