Fix generating fields color to proper rendering svg->pdf for asciidoc flow

[iDoka]

The both, wavedrom and wavedrompy use hsl representation of colors for bitfield functionaluty.
It seems asciidoctor flow doesn't support hsl in svg well.

The svg files from wavedrom and wavedrompy rendering in Chrome:

The same svg from wavedrom and wavedrompy build in asciidoc and finally rendered as PDF:

I tried to make tiny fix to convert HSL->RGB:

iDoka@90dffcd

[wallento]

Thanks. I have cherry-picked that commit for inclusion in the next relase!