Fix season_type for extended regular season

[mrcaseb]

It looks like the extended reg season only affects this line

nflfastR/R/helper_scrape_nfl.R

Line 61 in 5af7e30

season_type <- dplyr::if_else(week <= 17, "REG", "POST")

as well as parts of the beginners guide vignette

nflfastR/vignettes/beginners_guide.Rmd

Line 312 in bfacba8

filter(week <= 17, !is.na(epa)) %>%

nflfastR/vignettes/beginners_guide.Rmd

Line 500 in bfacba8

filter(rush == 1 | pass == 1, week <= 17, !is.na(epa), !is.na(posteam), posteam != "") %>%

Although the examples in the beginners guide use seasons where it is safe to filter week, I think it's better to use season_type so people learn to work with it.