clippy 0.0.208

A bunch of helpful lints to avoid common pitfalls in Rust
error: using `writeln!(v, "")`
 --> $DIR/writeln_empty_string.rs:9:5
  |
9 |     writeln!(&mut v, "");
  |     ^^^^^^^^^^^^^^^^^^^^ help: replace it with: `writeln!(v)`
  |
  = note: `-D write-with-newline` implied by `-D warnings`

error: aborting due to previous error