minor edits to test-mcmc.R
minor edits to test-mcmc.R

NLMichaud/nimble,nimble-dev/nimble,NLMichaud/nimble,nimble-dev/nimble,nxdao2000/nimble,nxdao2000/nimble,nimble-dev/nimble,NLMichaud/nimble,nimble-dev/nimble,NLMichaud/nimble,nimble-dev/nimble,nxdao2000/nimble,nxdao2000/nimble