Okay… Since std:accounts is pinned to 1.0.10, you can try to add firstname.lastname@example.org! to your .meteor/packages file. There is a good possibility that this isn’t going to work since the constraint resolver is going to try to save you from yourself. If this is the case then the only option at that point is to get the author to update their package to support the latest version of Meteor, or clone it into your local packages dir and update the constraint yourself.
I have changed email package version to 2.0.0 in my .meteor/packages file and ran the meteor update command, but getting the same error, will try to clone the package in local folder and update the constraint.