update implementation of fontbakery-fix-vertical-metrics.py
update implementation of fontbakery-fix-vertical-metrics.py

to conform to new codebase style

moyogo/fontbakery,moyogo/fontbakery,graphicore/fontbakery,graphicore/fontbakery,googlefonts/fontbakery,googlefonts/fontbakery,graphicore/fontbakery,moyogo/fontbakery,googlefonts/fontbakery