我做了什么：
$ sudo add-apt-repository ppa:elementary-os/stable
$ sudo apt update
Ubuntu 18.04.3 Mate 尝试安装 Pantheon-Files 但出现错误：
$ sudo apt-get install -f pantheon-files
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
pantheon-files : Depends: libcloudproviders0 (>= 0.3.0) but it is not going to be installed
Recommends: contractor but it is not going to be installed
Recommends: tumbler-plugins-extra but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
尝试过其他方式，例如 snap 或 flatpak 或 appimage，但没有运气。
