losen pep8 version check
losen pep8 version check

Summary:
pep8 has used both 2 (`1.2`) and 3 (`1.2.1`) digit versions.  Losen
the version check to allow for both.

NOTE: This is the same regex as flake8.

Test Plan: `arc unit` with a 2 and 3 digit pep8 version on `$PATH`.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: joshuaspence, epriestley

Differential Revision: https://secure.phabricator.com/D11728

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