in docker, just use npm to avoid complexity

.gitignore

@@ -62,3 +62,6 @@ npm-debug.log
 # In case we want to keep something in the compiled assets directory
 !/app/assets/builds/.keep
 .aider*
+
+# ignore package-lock.json for now, but someday we will switch from yarn to npm
+package-lock.json

Dockerfile

@@ -25,15 +25,12 @@ RUN apk update && apk upgrade && apk add --update --no-cache \
   postgresql-client \
   tzdata \
   vim && rm -rf /var/cache/apk/*
-# The ruby alpine image's apk doesn't have the current version of node
-RUN apk add  --no-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/main/ nodejs npm
 
 WORKDIR $RAILS_ROOT
 
 COPY . .
-RUN npm install --global yarn
-RUN yarn install
-RUN yarn build && yarn build:css
+RUN npm install
+RUN npm build && npm build:css
 
 COPY --from=builder /usr/local/bundle/ /usr/local/bundle/