p5-String-Compare-ConstantTime: update to 0.320.

0.320  2018-04-22
  * Added Travis and Appveyor testing (thanks Paul Cochrane)
  * Use warnings pragmas (thanks Paul Cochrane)
  * Many documentation and meta-data fixes/updates (thanks Paul Cochrane)
  * Better test coverage for strings with/without utf8 flag
    (thanks Paul Cochrane)
  * Replace SvCUR with sv_len_utf8 to work around issue in debugging
    versions of perl (see https://github.com/hoytech/String-Compare-ConstantTime/issues/4)
    (thanks Paul Cochrane)

(wiz)