Fix license: "PDDL-1.0"

Reading composer.json of dkrnl/simplexmlreader (master)
Skipped branch master, Invalid package information:
License "Public Domain" is not a valid SPDX license identifier, see https://spdx.org/licenses/ if you use an open license.
If the software is closed-source, you may use "proprietary" as license.

from issue

#9