wrong URLs generated for vignette sources

[IndrajeetPatil]

All sources for .Rmd files point to rdocumentation webpage for arithmetic in R.

Here is a preview of this error for ggstatsplot package website (https://indrajeetpatil.github.io/ggstatsplot/)-

[jayhesselberth]

dup of #889

[jayhesselberth]

Re-opening for reference.

[jayhesselberth]

Seems to be fixed by #896