Fix duplicate code chunk label

Author: wlandau-lilly

vignettes/parallelism.Rmd

@@ -154,7 +154,7 @@ make(my_plan, parallelism = "future_lapply")
 
 This approach should allow you to deploy targets to a [Docker container](https://www.docker.com/what-container).
 
-```{r owncluster, eval = FALSE}
+```{r ownclusterdocker, eval = FALSE}
 ## Setup of Docker worker running rocker and r-base
 ## (requires installation of future package)
 cl <- future::makeClusterPSOCK(