Error on Windows

[Shinyu Murakami]

See: vivliostyle/vivliostyle-cli#72

There are two problems:

• Can't find "gs" command on Windows even if ghostscript is installed
  • Reason: Ghostscript CLI for Windows is installed as C:\Program Files\gs\gs9.52\bin\gswin64c.exe
• Windows path name with backslashes is not properly passed to the ghostscript command options.
  • e.g.,

    press-ready/src/ghostScript.ts

    Line 90 in 37e48e2

     `-sOutputICCProfile=${iccProfilePath}` 

    causes error when iccProfilePath contains backslashes

[Shinyu Murakami]

I'm working on fixing it.