address situation when nsubjects is a vector of length > 1

[sbanville-delfi]

The cps.binary function gives an error when running the second example from the documentation. This occurs when nsubjects is a vector of length > 1.

This example

binary.sim2 <-
  cps.binary(
    nsim = 100,
    nsubjects = c(c(rep(10,9),100), rep(20,10)),
    nclusters = 10,
    p1 = 0.8,
    p2 = 0.5,
    sigma_b_sq = 1,
    sigma_b_sq2 = 1.2,
    alpha = 0.05,
    method = 'gee',
    allSimData = FALSE
)

outputs the following error:

Error in cps.binary(nsim = 100, nsubjects = c(c(rep(10, 9), 100), rep(20,  : 
  could not find function "cps.binary"

This PR addresses this by requiring all elements of nsubjects to meet the requirements.