Make multiple RUN commands explicit in Dockerfile

Dockerfile

@@ -4,7 +4,8 @@ ARG BUILD_PACKAGES="build-base git"
 ARG DEV_PACKAGES="postgresql-dev yarn"
 ARG RUBY_PACKAGES="tzdata"
 
-RUN apk update && apk add --no-cache $BUILD_PACKAGES $DEV_PACKAGES $RUBY_PACKAGES
+RUN apk update && \
+      apk add --no-cache $BUILD_PACKAGES $DEV_PACKAGES $RUBY_PACKAGES
 
 RUN mkdir /app
 WORKDIR /app