fix: /ip should not include port number

[mccutchen]

Fixes #211

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.51%. Comparing base (3855b88) to head (0bde92b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #212      +/-   ##
==========================================
+ Coverage   94.50%   94.51%   +0.01%     
==========================================
  Files          10       10              
  Lines        2239     2244       +5     
==========================================
+ Hits         2116     2121       +5     
  Misses         86       86              
  Partials       37       37              

Files with missing lines	Coverage Δ
httpbin/helpers.go	96.19% <100.00%> (+0.04%)	⬆️

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