Fixed t/20-zombie.t ..... Can't locate Time/HiRes.pm in @INC on run make test

```bash
Fixed t/20-zombie.t ..... Can't locate Time/HiRes.pm in @INC (@INC contains: /opt/github/System-Command/blib/lib /opt/github/System-Command/blib/arch /usr/local/lib/perl5 /usr/local/share/perl5 /usr/lib/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib/perl5 /usr/share/perl5 .) at t/20-zombie.t line 6.
BEGIN failed--compilation aborted at t/20-zombie.t line 6.

Test Summary Report
-------------------
t/20-zombie.t   (Wstat: 512 Tests: 0 Failed: 0)
  Non-zero exit status: 2
  Parse errors: No plan found in TAP output

Added skip tests if Time::HiRes not found.
```