fix: invalid value 0 for 'digits' argument

[mcanouil]

Since R 4.2.0, digits arguments of format() is constrained to be higher or equal to 1. nsmallset to zero should be enough to get the requested "integer" format.

This PR, ensures digits is at least 1 in print_ctable().

fixes #163

• master branch (current behaviour)

  data("tobacco")
  ctable(tobacco$gender, tobacco$smoker, round.digits = 0)
  #> Error in prettyNum(.Internal(format(x, trim, digits, nsmall, width, 3L,  : 
  #>  invalid value 0 for 'digits' argument
  

• PR

  data("tobacco")
  ctable(tobacco$gender, tobacco$smoker, round.digits = 0)
  #> Cross-Tabulation, Row Proportions  
  #> gender * smoker  
  #> Data Frame: tobacco  
  #> 
  #> -------- -------- ----------- ----------- -------------
  #>            smoker         Yes          No         Total
  #>   gender                                               
  #>        F            147 (30%)   342 (70%)    489 (100%)
  #>        M            143 (29%)   346 (71%)    489 (100%)
  #>     <NA>              8 (36%)    14 (64%)     22 (100%)
  #>    Total            298 (30%)   702 (70%)   1000 (100%)
  #> -------- -------- ----------- ----------- -------------------