harfbuzz: update to 2.1.3.

Overview of changes leading to 2.1.3
Friday, November 16, 2018
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- Fix AAT 'mort' shaping, which was broken in 2.1.2

Overview of changes leading to 2.1.2
Friday, November 16, 2018
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- Various internal changes.
- AAT shaping improvements:
  o Implement kern table Format 1 state-machine-based kerning.
  o Implement cross-stream kerning (cursive positioning, etc).
  o Ignore emptyish GSUB tables (zero scripts) if morx present.
  o Don't apply GPOS if morx is being applied.  Matches Apple.

(wiz)