www/firefox-esr: update to 45.6.0 (rc1)

Changes: https://www.mozilla.org/firefox/45.6.0/releasenotes/
Changes: https://hg.mozilla.org/releases/mozilla-esr45/shortlog
Security: 512c0ffd-cd39-4da4-b2dc-81ff4ba8e238
MFH: 2016Q4