We have published a pretty basic extension which solves an irritating issue for Magento 2 users.

For popup login in Magento 2, this extension replaces strings "Checkout out as a new customer" and "Checkout out using your account" with "Checkout as a new customer" and "Checkout using your account" respectively.

This is such a small issues that it should have been fixed in magento long ago, but unfortunately it still persists from Magento 2.0 till Magento 2.2.3.

More details on Github.