message: bump syn to 0.15.29
  (older versions didn't have the `syn::Result` type, it seems?)
diff: @@ -15,5 +15,5 @@ proc-macro = true
  heck = "0.3"
  proc-macro2 = "0.4"
  quote = "0.6"
  -syn = { version = "0.15", features = ["full", "extra-traits"] }
  +syn = { version = "0.15.29", features = ["full", "extra-traits"] }
  