I have the same problem after installing quickstart.
On a test server with PHP 5.4. I get the error
Fatal error: Can't use method return value in write context in .../plugins/content/quix/quix.php on line 124
On another server with PHP 5.6 I get the error
Parse error: syntax error, unexpected '?' in .../libraries/quix/vendor/illuminate/support/Arr.php on line 293
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