Bug#950901: ruby-fakefs: missing ruby2.7 support

[Cédric Boutillier]

Package: ruby-fakefs
Version: 0.20.1-1
Severity: important
Tags: upstream
Control: forwarded -1 https://github.com/fakefs/fakefs/issues/437

Dear Maintainer,

This library still does not support ruby2.7.
More investigation is needed.