fix js client

[pepegar]

This PR fixes 2 different bugs:

1. exampleJS project was failing to link because cats-effect wasn't included for JS (it used %% instead of %%%)
2. MatchError when parsing empty headers from XHR response.

fixes #91 and #90

[codecov]

Codecov Report

Merging #92 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #92   +/-   ##
=======================================
  Coverage   65.11%   65.11%           
=======================================
  Files          22       22           
  Lines         579      579           
  Branches       10       10           
=======================================
  Hits          377      377           
  Misses        202      202

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[pepegar]

Ignoring Codacy for now, since most of the issues are style related and code style is not aligned with what we use here.