fix typo in troubleshoot-app-health.html
fix typo in troubleshoot-app-health.html

shalako/docs-dev-guide,logit-io/docs-dev-guide,summerzhao/docs-dev-guide,cloudfoundry/docs-dev-guide,bridgetkromhout/docs-dev-guide,krujos/docs-dev-guide,cwest/docs-dev-guide