Use correct index when parsing publicHost

[phairoh]

2.4.3 introduced checking of the host header and options for setting the public host however when parsing the publicHost it was still using the index of : from the host header hostname. This corrects that.

[codecov]

Codecov Report

Merging #888 into master will increase coverage by 1.6%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #888     +/-   ##
=========================================
+ Coverage   72.01%   73.62%   +1.6%     
=========================================
  Files           4        4             
  Lines         436      436             
  Branches      130      130             
=========================================
+ Hits          314      321      +7     
+ Misses        122      115      -7

Impacted Files	Coverage Δ
lib/Server.js	83% <100%> (+2.33%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7d08d1e...f26f985. Read the comment docs.

[phairoh]

Added a few tests for the checkHost method. Validation.test.js seemed like the proper place for these but I wasn't entirely sure.

[sokra]

Thanks