Upgrade 0.6.1 to 0.7.1 not working

Baikal version: 0.6.1 -> 0.7.1

[X] I have searched open and closed issues for duplicates
[X] I have installed the release zip, not the source code zip
[ ] I have moved the whole, untouched Specific and config folders to the new installation

Problem: I unzipped 0.7.1, moved the "Specific" folder (there is no "config" folder in 0.6.1) and started the installer. During the setup it asked some questions (timezone etc.). The MySQL part was pre-filled but after submitting the form the values weren't saved to the config file. So I added it manually and I could trigger the upgrade process with a successful message. -> Admin Login works fine. -> CalDAV and CardDAV are not working.

So I tried to check what the server answers to my mobile devices and called the URL in the Webbrowser: https:///cal.php/principals/

ParseError: syntax error, unexpected 'const' (T_CONST), expecting variable (T_VARIABLE) in /var/www/baikal-0.7.1/vendor/sabre/dav/lib/DAV/Version.php:19
Stack trace:
#0 /var/www/baikal-0.7.1/vendor/composer/ClassLoader.php(322): Composer\Autoload\includeFile('/var/www/baikal...')
#1 [internal function]: Composer\Autoload\ClassLoader->loadClass('Sabre\\DAV\\Versi...')
#2 /var/www/baikal-0.7.1/vendor/sabre/dav/lib/DAV/Server.php(269): spl_autoload_call('Sabre\\DAV\\Versi...')
#3 /var/www/baikal-0.7.1/vendor/sabre/dav/lib/DAV/Server.php(319): Sabre\DAV\Server->start()
#4 /var/www/baikal-0.7.1/Core/Frameworks/Baikal/Core/Server.php(119): Sabre\DAV\Server->exec()
#5 /var/www/baikal-0.7.1/html/cal.php(74): Baikal\Core\Server->start()
#6 {main}

I don't know what the issue is and reverted to baikal 0.6.1.

sabre-io / Baikal

Upgrade 0.6.1 to 0.7.1 not working #948