chore: removed useless apt-get update from backend Dockerfile, included package-lock

backend/Dockerfile

@@ -1,12 +1,11 @@
 FROM node:15
 
-RUN apt-get update
-
 RUN npm install -g nodemon
 
 RUN mkdir -p /opt
 WORKDIR /opt
 ADD package.json /opt/package.json
+ADD package-lock.json /opt/package-lock.json
 
 RUN npm install