Replaced i18n with tpl in GhostMailer.js (#13555)
Replaced i18n with tpl in GhostMailer.js (#13555)

refs: #13380

- The i18n package is deprecated. It is being replaced with the tpl package.
janvt/Ghost,e10/Ghost,ErisDS/Ghost,TryGhost/Ghost,TryGhost/Ghost,janvt/Ghost,e10/Ghost,ErisDS/Ghost,TryGhost/Ghost,ErisDS/Ghost