Update a chunk in the RI2 guide

[jwbowers]

@acoppock We've been recompiling guides and ran into a problem here. We had to remove the plot to get it to run through --- and the summary shows NAs. We'd like to have the nice plot again. Any ideas about what we should do? (I changed condition_names to conditions to update the call to declare_ra FYI.) The chunk starts on line 196 and is in the section headed # 7. Randomization inference for multi-arm trials

three_arm_dat <- read.csv("three_arm_dat.csv")
three_arm_dec <- declare_ra(N = 200, 
                            conditions = c("Control", "Treatment 1", "Treatment 2"))

ri_out <-
    conduct_ri(
      formula = Y ~ Z,
      declaration = three_arm_dec,
      data = three_arm_dat,
      sims = sims
    )


summary(ri_out)
## plot(ri_out)

[jwbowers]

More info from brilliant Georgiy Syunyaev

"the place where this happens is in the function ri2:::conduct_conditional_ra()

specifically in 

assignment_vec_new[assignment_vec %in% conditions] <- complete_ra(N = sum(assignment_vec %in% 
      conditions), prob_each = prob_each_local, conditions = conditions, 
      check_inputs = FALSE)

and similar chunks of code (there are a bunch of them) 

at that point basically all "Treatment 1"/"Treatment 2" get by accident converted into "1"/“2""