Fix bug

Author: davidanthoff

src/rendering/show.jl

@@ -9,7 +9,7 @@ function convert_vl_to_x(v::VLSpec, fileformat)
     reader = @async read(p, String)
     wait(p)
     res = fetch(reader)
-    if p.processes[1].exitcode != 0 || p.processes[2].exitcode != 0
+    if p.exitcode != 0
         throw(ArgumentError("Invalid spec"))
     end
     return res