Example assumes MTS is installed

[MichaelChirico]

fable/R/VARIMA.R

Lines 177 to 178 in 70e55ac

	#' fit <- aus_production %>%
	#' model(VARIMA(vars(Beer, Cement) ~ pdq(4,1,1), identification = "none"))

Without MTS we get a somewhat unpalatable failure:

> library(tsibbledata)
> aus_production %>% autoplot(vars(Beer, Cement))
> fit <- aus_production %>% model(VARIMA(vars(Beer, Cement) ~ pdq(4, 1, 
+     1), identification = "none"))
Warning: 1 error encountered for VARIMA(vars(Beer, Cement) ~ pdq(4, 1, 1), identification = "none")
[1] The `MTS` package must be installed to use this functionality. It can be installed with install.packages("MTS")

> fit
# A mable: 1 x 1
  `VARIMA(vars(Beer, Cement) ~ pdq(4, 1, 1), identification = "none")`
                                                               <model>
1                                                         <NULL model>
> ## End(Don't show)
> ## Don't show: 
> if (requireNamespace("tsibbledata", quietly = TRUE)) (if (getRversion() >= "3.4") withAutoprint else force)({ # examplesIf
+ ## End(Don't show)
+ 
+ fit %>%
+   forecast(h = 50) %>%
+   autoplot(tail(aus_production, 100))
+ ## Don't show: 
+ }) # examplesIf
> fit %>% forecast(h = 50) %>% autoplot(tail(aus_production, 100))
Error in FUN(X[[i]], ...) : 
  attempt to set 'colnames' on an object with less than two dimensions

Only from staring at this sort of log for long enough was I able to piece together what's gone wrong.

Related: #432