qt: Don't use QDateTime::toSecsSinceEpoch
qt: Don't use QDateTime::toSecsSinceEpoch

* lang/qt/src/qgpgmequickjob.cpp (addSubkeyWorker)
(createWorker): Use toMSecsSinceEpoch instead toSecsSinceEpoch.

--
toSecsSinceEpoch was only introduced in Qt 5.8.

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