"DeviceDetector could not be found"

So my hosting plan crashed during an auto update causing error messages. Some files from the install were incomplete uploads and I manually FTPed them in place. Now the error messages are gone, but this text greets me:

DeviceDetector could not be found, maybe you are using Piwik from git and need to update Composer. Execute this command: php composer.phar update

Any idea how I could address this? I never used the git, and I am not sure what the error is about.

I just got this today too, easiest solution for me was following the manual update process - backup config, download latest release and ftp it overwriting the existing installation.