Change to which instead of whereis

[lachieh]

Removes the insecure dep whereis and changes to which. Functionality is a straight swap, so no changes need to be updated.

Fixes #208

[codecov-io]

Codecov Report

Merging #220 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #220   +/-   ##
=======================================
  Coverage   81.34%   81.34%           
=======================================
  Files          26       26           
  Lines         563      563           
  Branches      103       92   -11     
=======================================
  Hits          458      458           
+ Misses         84       81    -3     
- Partials       21       24    +3

Impacted Files	Coverage Δ
packages/ssh-pool/src/commands/rsync.js	62.96% <100%> (ø)	⬆️
packages/ssh-pool/src/commands/tar.js	65.21% <0%> (ø)	⬆️
packages/ssh-pool/src/commands/raw.js	68.75% <0%> (ø)	⬆️

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[gregberge]

Thanks!