message: add rust-version
diff: @@ -12,6 +12,7 @@ homepage = "https://github.com/ramsayleung/rspotify"
  repository = "https://github.com/ramsayleung/rspotify"
  keywords = ["spotify", "api"]
  edition = "2021"
  +rust-version = "1.56"
  [workspace]
  members = [
  @@ -22,9 +23,6 @@ members = [
  exclude = [
  "examples/webapp"
  ]
  -# For advanced features usage in the CLI, see:
  -# https://doc.rust-lang.org/nightly/cargo/reference/features.html#resolver-version-2-command-line-flags
  -resolver = "2"
  [dependencies]
  rspotify-macros = { path = "rspotify-macros", version = "0.11.3" }
  