Comment 58 for bug 1717040

I've got an explanation for the "DOWNGRADED" statement :
I had ppa:ginggs/backports in my list of ppa.
This ppa contains an updated version of zstd.
So that's why when applying `apt-get install zstd/xenial-proposed`, it features the "DOWNGRADED" statement.

Removing the PPA, and re-installing the default zstd v0.5.1 from Xenial, I now get :
```
sudo apt install zstd/xenial-proposed
Reading package lists... Done
Building dependency tree
Reading state information... Done
Selected version '1.3.1+dfsg-1~ubuntu0.16.04.1' (Ubuntu:16.04/xenial-proposed [amd64]) for 'zstd'
Selected version '5.4.0-6ubuntu1~16.04.9' (Ubuntu:16.04/xenial-proposed [amd64]) for 'libstdc++6' because of 'zstd'
The following additional packages will be installed:
  libzstd1
The following NEW packages will be installed:
  libzstd1
The following packages will be upgraded:
  zstd
1 upgraded, 1 newly installed, 0 to remove and 157 not upgraded.
Need to get 0 B/391 kB of archives.
After this operation, 905 kB of additional disk space will be used.
```

which is the expected outcome.

then :
```
zstd -V
*** zstd command line interface 64-bits v1.3.1, by Yann Collet ***
```