Update to 68.2.0 with patch from Piotr Meyer

Changelog:
Security fixes:
#CVE-2019-15903: Heap overflow in expat library in XML_GetCurrentLineNumber
#CVE-2019-11757: Use-after-free when creating index updates in IndexedDB
#CVE-2019-11758: Potentially exploitable crash due to 360 Total Security
#CVE-2019-11759: Stack buffer overflow in HKDF output
#CVE-2019-11760: Stack buffer overflow in WebRTC networking
#CVE-2019-11761: Unintended access to a privileged JSONView object
#CVE-2019-11762: document.domain-based origin isolation has same-origin-property violation
#CVE-2019-11763: Incorrect HTML parsing results in XSS bypass technique
#CVE-2019-11764: Memory safety bugs fixed in Firefox 70 and Firefox ESR 68.2

(ryoon)