fix: type extension_id in X509.Certificate.Extension

[DavidGonzalezPineiro]

Resolves #82

Description

There seems to be an issue with the @type extension_id definition in X509.Certificate.Extension. Specifically, the atom :crl_distribution_point is used in the type, but it should be :crl_distribution_points.

This causes Dialyzer to fail when calling:

X509.Certificate.Extension.find(cert_extensions, :crl_distribution_points)

The error reported by Dialyzer is as follows:

The function call will not succeed.

X509.Certificate.Extension.find(_cert_extensions :: [any()], :crl_distribution_points)

breaks the contract
([t()], extension_id() | :public_key.oid()) :: t() | nil