Writer produces incorrect code for StringPattern

[MartinSStewart]

This code

StringPattern "test"
    |> Node emptyRange
    |> Writer.writePattern
    |> Writer.write

produces test instead of "test".

This causes problems in case expressions where instead of generating

toString : MyType -> String
toString value =
    "Variant1" -> Variant1

elm-syntax's writer generates

toString : MyType -> String
toString value =
    Variant1 -> Variant1