Dockerfile: fix build 🐛, optimize layer caching

Dockerfile

@@ -1,22 +1,31 @@
 FROM node:alpine as builder
 WORKDIR /app
 
+# install dependencies
 RUN apk add --update git bash
-
 ADD package.json /app
-RUN npm install --production
+RUN npm install
+
+# build documentation
+ADD . /app
+RUN npm run build
+
+# ---
 
 FROM node:alpine
 WORKDIR /app
 
+# install dependencies
+ADD package.json /app
+RUN npm install --production
+
+# add source code
+ADD . /app
+COPY --from=builder /app/docs ./docs
+
 EXPOSE 3000
 
 ENV HOSTNAME v5.db.transport.rest
 ENV PORT 3000
 
-COPY --from=builder /app/node_modules ./node_modules
-ADD . /app
-
-RUN npm run build
-
 CMD ["node", "index.js"]