isCA check error, noticed when using typescript

[agmcleod]

I think the line here:

webauthn-demo/utils.js

Line 259 in a32c36c

!pem.extensions.isCA &&

is incorrect. I've been pulling in some of this code into a demo/prototype project. I'm using typescript, and was able to reference the types for the x509 package. The typescript compiler noted how isCA is not a field on the Extension[] field. I think this can be changed to use the isCA field on the pem object instead. The library sifts through the extensions and updates the boolean based on what it finds here: https://github.com/fidm/x509/blob/master/src/x509.ts#L393