Fontmake

- [instantiator] Fixed bug whereby "bracket" glyphs (i.e. those substituted through DesignSpace rules) were losing all the anchors, and thus were getting excluded from `mark`, `mkmk` etc. features (632).

**NOTE**: It is recommended that you rebuild your fonts if you used "bracket" layers or DesigSpace rules, and these glyphs contained any anchors that were meant to produce mark/mkmk features.

* glyphsLib >= 4.0.0

Restrict fontmake to use a compatible version of glyphsLib (~=5) in
anticipation of upcoming major glyphsLib 6 release, to prevent potential
regressions.