multiline input for mermiad.js graphs

[wlandau]

Would it be possible to allow multiline input for mermaid.js graphs? I find it convenient to keep a mermaid.js graph as a character vector of lines:

graph <- c(
  "graph LR",
  "  subgraph Legend",
  "    outdated([Outdated]):::outdated --- stem([Stem]):::none",
  "    stem([Stem]):::none --- function>Function]:::none",
  "  end", 
  "  subgraph Graph", "    g>g]:::outdated --> f>f]:::outdated", 
  "    y1([y1]):::outdated --> z([z]):::outdated",
  "    y2([y2]):::outdated --> z([z]):::outdated", 
  "    f>f]:::outdated --> y1([y1]):::outdated",
  "  end",
  "  classDef outdated stroke:#000000,color:#000000,fill:#78B7C5;", 
  "  classDef none stroke:#000000,color:#000000,fill:#94a4ac;", 
  "  linkStyle 0 stroke-width:0px;",
  "  linkStyle 1 stroke-width:0px;"
)

After installing 91059fd and then updating mermaid.js using #421 (comment), I can generate the desired graph if I paste the lines together.

DiagrammeR::mermaid(paste0(graph, collapse = "\n"))

But if I do not paste the lines, I see this:

Mermaid graphs have been great for targets: ropensci/targets#802