message: revert gumdrop to 0.7.x
diff: @@ -20,7 +20,7 @@ blake2b_simd = "0.5.10"
  base64 = "0.13.0"
  hex = { git = "https://github.com/Zondax/rust-hex", rev="6e35fb48999278c8c6c75b099baa4ea2a9d1d12b" }
  -gumdrop = "0.8.0"
  +gumdrop = "0.7.0"
  [dependencies.abscissa_core]
  version = "0.5.2"
  