message: Fix test on windows
  Backslashes here are escaped (\\), so [/] does not really help :(
diff: @@ -3269,5 +3269,5 @@ fn no_bin_in_src_with_lib() {
  assert_that(p.cargo_process("build"),
  execs().with_status(101)
  - .with_stderr_contains(r#"[ERROR] couldn't read "src[/]bin[/]main.rs"[..]"#));
  + .with_stderr_contains(r#"[ERROR] couldn't read "[..]main.rs"[..]"#));
  }
  