Error: SSL certificate problem - Sankey Diagram

Can you please address this issue?
I've successfully run the sample code from https://rdrr.io/cran/networkD3/f/README.md up to the Sankey Diagram:

> # Recreate Bostock Sankey diagram: http://bost.ocks.org/mike/sankey/
> # Load energy projection data
> URL <- paste0("https://cdn.rawgit.com/christophergandrud/networkD3/",
+ "master/JSONdata/energy.json")
> Energy <- jsonlite::fromJSON(URL)
Error in open.connection(con, "rb") :
SSL certificate problem: certificate has expired
>
> # Plot
> sankeyNetwork(Links = Energy$links, Nodes = Energy$nodes, Source = "source",
+ Target = "target", Value = "value", NodeID = "name",
+ units = "TWh", fontSize = 12, nodeWidth = 30)
Error in is.factor(Source) : object 'Energy' not found