Fix rule_checker example
Fix rule_checker example

-ruleFile doesn’t exist, and the existing -rule-file flag is deprecated in https://github.com/prometheus/prometheus/commit/c4e762adbf6ee7f8fd24af8dc584a64d14974a7e
jimmidyson/docs,ChaoticMind/docs,open-falcon/open-falcon.github.io,du2016/prometheus-docs,ChaoticMind/docs,dln/docs,Cepave/openfalcon.io,open-falcon/open-falcon.github.io,fabxc/docs,ddfreyne/prometheus-docs,vic3lord/docs,ddfreyne/prometheus-docs,dato/prometheus-docs,du2016/prometheus-docs,tcolgate/docs,bluecmd/prometheus-docs,vic3lord/docs,jimmidyson/docs,evanphx/docs,evanphx/docs,chosenken/docs,tcolgate/docs,du2016/prometheus-docs,Cepave/openfalcon.io,ChaoticMind/docs,ddfreyne/prometheus-docs,tcolgate/docs,dln/docs,prometheus/docs,dato/prometheus-docs,jmptrader/docs,Cepave/openfalcon.io,jmptrader/docs,dato/prometheus-docs,fabxc/docs,chosenken/docs,evanphx/docs,vic3lord/docs,ddfreyne/prometheus-docs,prometheus/docs,pdbogen/docs,dln/docs,jimmidyson/docs,chosenken/docs,open-falcon/open-falcon.github.io,chosenken/docs,bluecmd/prometheus-docs,pdbogen/docs,fabxc/docs,bluecmd/prometheus-docs,prometheus/docs,jmptrader/docs,pdbogen/docs