fix: anchor domain regex in validateIp to reject trailing input

[lissy93]

Hey @dopecodez

Noticed that on the hostname check, it correctly matches a valid prefix, but ignored anything after that.
So this pr just adds $ to the end of the regex to anchor it at the end too

e.g. previously a.co; rm -rf / was passing validation.
This isn't a security issue, since pingman correctly runs the ping via a spawn. But just thought we could neaten it up, and add some defence in depth so that we throw the ERROR_MESSAGES.IP_NOT_VALID message much earlier

Also added a unit test for this :)

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.70%. Comparing base (bc1708d) to head (d4acdd4).
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Additional details and impacted files

@@           Coverage Diff           @@
##           master      #58   +/-   ##
=======================================
  Coverage   78.70%   78.70%           
=======================================
  Files          14       14           
  Lines         385      385           
  Branches      116      116           
=======================================
  Hits          303      303           
  Misses          3        3           
  Partials       79       79           

Files with missing lines	Coverage Δ
src/helper.ts	100.00% <100.00%> (ø)

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[dopecodez]

Thanks for the MR @lissy93 🥇 . The older regex was ignoring everything after the match, so this is a much better check to have.

[dopecodez]

A new build with these changes have been released - v2.2.0 on github or the latest on npm. Thanks again for the changes @lissy93 🐐