tests: Fix some warning in the test crate.

Author: emilio

tests/expectations/build.rs

@@ -37,7 +37,7 @@ fn main() {
                 .to_string()
                 .chars()
                 .map(|c| match c {
-                    'a'...'z' | 'A'...'Z' | '0'...'9' => c,
+                    'a'..='z' | 'A'..='Z' | '0'..='9' => c,
                     _ => '_',
                 })
                 .collect();

tests/tests.rs

@@ -11,7 +11,7 @@ use std::fs;
 use std::io::{self, BufRead, BufReader, Error, ErrorKind, Read, Write};
 use std::path::PathBuf;
 use std::process;
-use std::sync::{Once, ONCE_INIT};
+use std::sync::Once;
 
 #[path = "../src/options.rs"]
 mod options;
@@ -23,7 +23,7 @@ static OVERWRITE_ENV_VAR: &str = "BINDGEN_OVERWRITE_EXPECTED";
 // Run `rustfmt` on the given source string and return a tuple of the formatted
 // bindings, and rustfmt's stderr.
 fn rustfmt(source: String) -> (String, String) {
-    static CHECK_RUSTFMT: Once = ONCE_INIT;
+    static CHECK_RUSTFMT: Once = Once::new();
 
     CHECK_RUSTFMT.call_once(|| {
         let have_working_rustfmt = process::Command::new("rustup")