use node:lts-alpine image for build jobs

node:alpine seems a little unstable for our purposes, so we stay with
LTS releases to be sure.

Dockerfile

 # stage-1: build dist folder
-FROM node:alpine as build
+FROM node:lts-alpine as build
 WORKDIR /usr/src/app
 COPY ["package.json", "package-lock.json", "/usr/src/app/"]
 RUN apk add python make g++