Bugfix fabric.PathGroup if object is not visible

- if object is not visible and of type 'path-group' the object was still drawn
JSHint - remove extra comma at the end of the fabric.Color.colorNameMap object
Merge pull request #469 from Kienz/GradientsSVGOutput

[BACK_INCOMPAT] Implement fabric.Gradient#toSVG() and radialGradient
Merge pull request #470 from Kienz/visiblePropFix

Bugfix fabric.PathGroup if object is not visible
Merge remote-tracking branch 'origins/master' into sketch
Build dist