- fix test suite with a chmod

- updated to 1.21
see /usr/share/doc/packages/perl-File-Which/Changes
1.21 2016-03-02 14:20:43 -0500
- Workaround for nutty cygwin filesystem rules

1.20 2016-03-01 15:06:54 -0500
- Fix bug where executable named "0" would not be found (gh#7)