bug: Disable colors for knitr markdown

[Fersoil]

When displaying info using the verbose_cat function the color codes are displayed as numeric values, which is unappealing in some cases, this error does not show up in the pkgdown wiki page

[ZetrextJG]

Maybe that happens because not all enviroments are capable of displaying color text. This is true for some older terminals, they simply cannot parse color codes thus no color