RFR: 8218020: Fix version number in mesa.md 3rd party legal file

[Roman Kennke]

Sort-of trivial version number update backport.

In contrast to >8 versions where the mesa version info is in a single
mesa3d.md file, the information is spread over several THIRD_PARTY_READY
in 8. See changesets here:

http://cr.openjdk.java.net/~rkennke/backport-jdk-JDK-8218020/

Original jdk12 bugfix:
http://hg.openjdk.java.net/jdk/jdk12/rev/cda5d1ed2c85
Issue:
https://bugs.openjdk.java.net/browse/JDK-8218020

Ok?

Roman