Make retrieving parents for mercurial commits work consistently across platforms
Make retrieving parents for mercurial commits work consistently across platforms

Summary:
Currently the template is single quoted, but Windows only supports double quotes. This meant that the output would be like:
  lang=text
  'aabbccddeeffaabbccddeeffaabbccddeeff0123
  '

Which is clearly wrong.

This is displayed like that in Phabricator as well, which is confusing.

Test Plan: ran `arc diff` on a Windows machine and saw the correct behaviour.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9450

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