Fontmake

Bumped minimum required [cu2qu >= 1.6.6](https://github.com/googlefonts/cu2qu/releases/tag/v1.6.6).
Fixes an issue while compiling variable font, when the last and first contour points have the same coordinates in some of the masters. cu2qu was incorrectly reporting different number of segments between glyphs.

https://github.com/googlefonts/cu2qu/pull/185
https://github.com/googlefonts/fontmake/issues/572

- [instantiator] Copy fontinfo attributes from the default font to instance selectively (excluding attributes that only apply for individual instance fonts, e.g. `styleName`, etc.) (578).
- [instantiator] Only copy non-kerning groups from default font; kerning groups proper are handled already by fontMath `MathKerning` class (579).
- Updated minimum requirements:

**ATTENTION: This release supports only Python 3.6+**

(Forgot to bump minimum versions of dependencies)

A new minimal instance generator to replace MutatorMath's Designspace reader and instance writer. It uses varLib instead of MutatorMath (so no anisotropic locations and extrapolation) and supports source layers for intermediate masters as well as Designspace rules for FeatureVariations-style glyph replacement.

Bugfixes

- Fixed issue when input ufo path has a trailing "/" at the end (393).
- Fixed issue whith `FDKFeatureCompiler` not working on POSIX platform (442).


Updated minimum requirements

- fonttools >= 3.27.1
- cu2qu >= 1.5.0
- glyphsLib >= 2.3.0
- ufo2ft >= 2.0.0
- MutatorMath >= 2.1.1
- defcon >= 0.5.1

A new minimal instance generator to replace MutatorMath's Designspace reader and instance writer. It uses varLib instead of MutatorMath (so no anisotropic locations and extrapolation) and supports source layers for intermediate masters as well as Designspace rules for FeatureVariations-style glyph replacement.