better handling of docker cache

Dockerfile

@@ -1,5 +1,7 @@
 FROM ubuntu:16.10
 
+WORKDIR /app
+
 EXPOSE 9050
 
 EXPOSE 53
@@ -22,12 +24,12 @@ RUN bash /tmp/nodejs_install
 
 RUN apt install -y --allow-unauthenticated deb.torproject.org-keyring nodejs tor git
 
-ADD . /app
-
-WORKDIR /app
+ADD package.json /app/package.json
 
 RUN npm install
 
+ADD . /app
+
 # Grab the current local timezone from an external api and save it into /etc/timezone, otherwise Tor will complain and won't start
 
 CMD bash /app/bin/get-timezone.sh > /etc/timezone && dpkg-reconfigure -f noninteractive tzdata && npm start