js: set expiry of generatedKey to seconds from now
js: set expiry of generatedKey to seconds from now

--

* src/Keyring.js: Changed key ecpiration from Date to seconds from
  creation, as in gpgme. The Date parameter used before was due to a
  misunderstanding in documentation and requests from potential users.

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme