v0.2.0

• Add Igniter task to support installing via mix igniter.install jump_credo_checks,
  courtesy of @britton-jb. #2
• Add new Jump.CredoChecks.PreferChangeOverUpDownMigrations check, which detects
  Ecto migrations that define separate up/down callbacks but could instead
  take advantage of Ecto's automatic reversibility by using change/0. #4