Stop using buffer-equal-constant-time

[idoshamun]

I noticed you use buffer-equal-constant-time indirectly through jws and gtoken.
buffer-equal-constant-time is a legacy and unsupported package since 2017. (salesforce/buffer-equal-constant-time#6)
It causes some issues in combination with docker and some other environments.
I'd appreciate if you can consider switching it.
A solid alternative for jwt purposes is fast-jwt.

I'm willing to work on it.

Related to googleapis/google-auth-library-nodejs#1544

[ddelgrosso1]

@idoshamun thank you for opening this issue. It seems like the better place to fix this would be in node-jwa which is what is actually importing buffer-equal-constant-time. It looks like there is already an open issue there as well: auth0/node-jwa#46.