message: use 'writeln' instead of appending newline character
diff: @@ -10,11 +10,11 @@ use std::fmt::Write;
  fn require(enabled_features: &[&str], disabled_features: &[&str]) -> String {
  let mut s = String::new();
  for feature in enabled_features {
  - write!(s, "#[cfg(not(feature=\"{feature}\"))] compile_error!(\"expected feature {feature} to be enabled\");\n",
  + writeln!(s, "#[cfg(not(feature=\"{feature}\"))] compile_error!(\"expected feature {feature} to be enabled\");",
  feature=feature).unwrap();
  }
  for feature in disabled_features {
  - write!(s, "#[cfg(feature=\"{feature}\")] compile_error!(\"did not expect feature {feature} to be enabled\");\n",
  + writeln!(s, "#[cfg(feature=\"{feature}\")] compile_error!(\"did not expect feature {feature} to be enabled\");",
  feature=feature).unwrap();
  }
  s
  