Log Message:
Updated p5-List-SomeUtils-XS to 0.55.

0.55     2017-07-23

- Skip all the tests unless List::SomeUtils 0.56 is installed. This fixes the
  issue where trying to install the new List::SomeUtils ends up pulling this
  distribution, which then fails because an older LSU is installed but doesn't
  export mode(). Reported by John SJ Anderson. GH #1.

0.54     2017-07-22

- Added a new function, mode(), requested by Jerrad Pierce. GH #2.