The alleged line is this one:
https://github.com/Chevereto/Installer/blob/master/index.php#L408
Key 1 means write permission, so basically the system is telling you that it doesn't have write permission on the Installer file.
I
will review the installer, but the fact that you have missing write permission makes impossible to install the software using the Installer script. The Installer can't fix missing permissions, is one layer above. Simply make sure that PHP has full read/write permission on / and in the installer file itself.
Cheers,
Rodolfo.