vdiffr 0.2.2

• Skip tests if the system version of Cairo (actually the one gdtools
  was compiled with) doesn't match the version of Cairo used to
  generate the testcases. Cairo has an influence on the computation of
  text metrics which can cause spurious test failures.

  We plan to fix these issues once and for all by embedding gdtools,
  svglite, Cairo and FreeType in the vdiffr package.