Bugfix: pem.extensions.isCA -> pem.isCA, remove 'new' before 'Buffer.from'

[magom001]

pem.extensions if an array and does not have isCA property. Statement always returns true.
Buffer.from is a factory method.

[codecov]

Codecov Report

Merging #37 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #37   +/-   ##
=======================================
  Coverage   12.66%   12.66%           
=======================================
  Files           5        5           
  Lines         387      387           
=======================================
  Hits           49       49           
  Misses        338      338           

Impacted Files	Coverage Δ
src/Webauthn.js	13.22% <ø> (ø)

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