php - rainloop curl not downloading

I'm trying to install Rainloop on my server.
In the documentation its sayed to download rainloop via the curl command
"curl -s https://repository.rainloop.net/installer.php | php".
When I enter this command nothing happens. And if I enter the command without the "-s" it only shows this:

% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed

0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0

It looks like the download won't even start. Since there is no error message I don't know what the error is.

Some technical Infos:
Ubuntu 16.04.2 LTS
Lamp stack is installed
Dovecot etc. also

Thanks for possible replys.