RUN: All chained commands should be parsed

[fhemberger]

RUN apk update \
  && apk add ca-certificates \ 
  && rm -rf /var/cache/apk/*

=> "Consider --no-cache or --update with rm -rf /var/cache/apk/* (Optimization)"

The parser should detect the rm -rf … in the third line.

RUN apk update \
  && rm -rf /var/cache/apk/*

=> No error message.