XSS vulnerability

[leonekmi]

Due to thephpleague/commonmark usage, Laravel-Markdown may be vulnerable to XSS attacks.
See thephpleague/commonmark#353

Solution is to update league/commonmark to ^0.18.3.

[GrahamCampbell]

Thanks for the report. We're not vulnerable, however, since composer will load the latest version. There would be no point in us increasing our minimum version requirement, because composer could just resolve an older version of this package if it really wanted to get 0.18.2.