Update mozjs68 to 68.12

[Amr Ibrahim]

Mozilla released Firefox ESR 68.12 to fix stability and security issues, and I think the mozjs68 SpiderMonkey engine is part of that. I don't know how severe the impact is of the security issues on Ubuntu since mozjs68 is not a full browser. I'll leave that to the security team to decide.

Mozilla Security Advisory:
68.12: https://www.mozilla.org/security/advisories/mfsa2020-37/
68.11: https://www.mozilla.org/security/advisories/mfsa2020-31/
68.10: https://www.mozilla.org/security/advisories/mfsa2020-25/
68.9: https://www.mozilla.org/security/advisories/mfsa2020-21/
68.8: https://www.mozilla.org/security/advisories/mfsa2020-17/
68.7: https://www.mozilla.org/security/advisories/mfsa2020-13/
68.6.1: https://www.mozilla.org/security/advisories/mfsa2020-11/