Merge pull request #707 from googlefonts/update-fontmake-3-8-1

requirements.txt: update fontmake to 3.8.1

resources/scripts/requirements.txt

@@ -1,7 +1,7 @@
 absl-py
 # keep fontmake version pinned to ensure output from ttx_diff.py is stable;
 # the 'repacker' option enables faster GSUB/GPOS serialization via uharfbuzz
-fontmake[repacker]==3.7.1
+fontmake[repacker]==3.8.1
 # technically fonttools is in turn a dependency of fontmake but a few of
 # our scripts import it directly, so we list it among the top-level requirements.
 fonttools