Bump FIREFOX_NIGHTLY to 67 (#1829)
Bump FIREFOX_NIGHTLY to 67 (#1829)

See https://github.com/mozilla-releng/ship-it/pull/250
La0/mozilla-relengapi,mozilla-releng/services,La0/mozilla-relengapi,La0/mozilla-relengapi,mozilla-releng/services,La0/mozilla-relengapi,mozilla-releng/services,mozilla-releng/services