Minor improvements to `ArcanistJSONLinter`
Minor improvements to `ArcanistJSONLinter`

Summary: Self-explanatory.

Test Plan: `arc unit`

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11324

memsql/arcanist,hach-que/arcanist,alexmv/arcanist,hach-que/arcanist,alexmv/arcanist,wikimedia/phabricator-arcanist,fivestars/arcanist,codelabs-ch/arcanist,wikimedia/phabricator-arcanist,folsom-labs/arcanist,sneakpeeq/arcanist,chundongwang/arcanist,zhihu/arcanist,wharris/arcanist,wharris/arcanist,KieranHayes/arcanist,phacility/arcanist,haskell-infra/arcanist,calblueprint/arcanist,PageUpPeopleOrg/arcanist-patches,uber/arcanist,aik099/arcanist,wxstars/arcanist,KieranHayes/arcanist,wxstars/arcanist,aik099/arcanist,eSpark/arcanist,codelabs-ch/arcanist,haskell-infra/arcanist,kevinseelbach/arcanist,codelabs-ch/arcanist,Symplicity/arcanist,r4nt/arcanist,Symplicity/arcanist,kevinseelbach/arcanist,calblueprint/arcanist,KieranHayes/arcanist,Khan/arcanist,folsom-labs/arcanist,Symplicity/arcanist,sneakpeeq/arcanist,jra3/arcanist,uber/arcanist,wharris/arcanist,phacility/arcanist,wharris/arcanist,sneakpeeq/arcanist,codelabs-ch/arcanist,alexmv/arcanist,coursera/arcanist,wxstars/arcanist,kevinseelbach/arcanist,uber/arcanist,Khan/arcanist,phacility/arcanist,coursera/arcanist,haskell-infra/arcanist,uber/arcanist,Khan/arcanist,codelabs-ch/arcanist,sneakpeeq/arcanist,wikimedia/phabricator-arcanist,r4nt/arcanist,zhihu/arcanist,kevinseelbach/arcanist,memsql/arcanist,jra3/arcanist,eSpark/arcanist,fivestars/arcanist,PageUpPeopleOrg/arcanist-patches,PageUpPeopleOrg/arcanist-patches,aik099/arcanist,wikimedia/phabricator-arcanist,jra3/arcanist,phacility/arcanist,coursera/arcanist,phacility/arcanist,calblueprint/arcanist,zhihu/arcanist,Symplicity/arcanist,r4nt/arcanist,PageUpPeopleOrg/arcanist-patches,memsql/arcanist,memsql/arcanist,folsom-labs/arcanist,KieranHayes/arcanist,wxstars/arcanist,chundongwang/arcanist,folsom-labs/arcanist,hach-que/arcanist,chundongwang/arcanist,chundongwang/arcanist,eSpark/arcanist,alexmv/arcanist,haskell-infra/arcanist,hach-que/arcanist,coursera/arcanist,eSpark/arcanist,fivestars/arcanist,zhihu/arcanist,r4nt/arcanist,jra3/arcanist,Khan/arcanist,calblueprint/arcanist,aik099/arcanist,fivestars/arcanist