bugfix for vendor autoload.php file path

[ctrl-f5]

No description provided.

[GrahamCampbell]

I don't think this is right?

[colinodell]

I think it is right. When installed as a Composer dependency you end up with these files:

├── composer.json
└── vendor
    ├── autoload.php
    ├── bin
    │   └── commonmark -> ../league/commonmark/bin/commonmark
    └── league
        └── commonmark
            └── bin
                └── commonmark

To access autoload.php from vendor/league/commonmark/bin/commonmark, you need to back out three levels to where autoload.php exists.

I merged a similar fix for league/html-to-markdown but didn't apply that here as well.

Thanks for contributing the fix!

[GrahamCampbell]

👍