Corrects incorrect header name used in basic authentication

[pandemonium]

I reported the bug. Please accept my attempt at fixing it.

[codecov]

Codecov Report

Merging #118 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master    #118   +/-   ##
======================================
  Coverage    69.4%   69.4%           
======================================
  Files          22      22           
  Lines         634     634           
  Branches        9       9           
======================================
  Hits          440     440           
  Misses        194     194

Impacted Files	Coverage Δ
core/shared/src/main/scala/hammock/Hammock.scala	71.42% <100%> (ø)	⬆️

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[pepegar]

Hey @pandemonium, thank you very much for both the bug report & the fix!