manifest: Update to freetype 2.6.0

The Freetype library in the Android source tree was outdated.
The old version had known security vulnerabilities and was updated
to 2.6.0 in AOSP master and tag android-m-preview-1.

Change-Id: I0df25091b868ed70fbe884f2613ad883329bc3f0
Ticket: CYNGNOS-676