Error for set_na()

[cschwem2er]

Hi,

I think during the change for the parameter name from value to na something went wrong. Although the parameter is listed as na`in the doc correctly, the following example raises an error:

x <- factor(c("a", "b", "c"))
x
set_na(x, na = "b", as.tag = TRUE)

Error in set_na(x, na = "b", as.tag = TRUE) : 
  argument "value" is missing, with no default

[sjPlot]

Forgot to change this:
https://github.com/sjPlot/sjmisc/blob/master/R/set_na.R#L117

value must be replaced by na in line 117 - will commit tonight.