Change PolyFill to support IOS

[MinisculeGirraffe]

Description

IOS does not support URLSearchParams(). Consequently any POST requests ran from an IOS device with this library fail.

Related Issues

Fixes Issue 372

Checklist:

• [X ] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [ X] Have you linted your code locally prior to submission?
• [ X] Have you successfully ran tests with your changes locally?

[codecov]

Codecov Report

Merging #373 into master will decrease coverage by 0.05%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #373      +/-   ##
==========================================
- Coverage   95.72%   95.67%   -0.06%     
==========================================
  Files          23       23              
  Lines         234      231       -3     
  Branches       21       21              
==========================================
- Hits          224      221       -3     
  Misses         10       10              

Impacted Files	Coverage Δ
src/util.js	66.66% <66.66%> (-4.17%)	⬇️

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[ddymko]

Closes #372