Update README example slightly

Fix bare_trait_objects warning.
Remove unnecessary mut borrows.

README.md

@@ -36,24 +36,24 @@ struct Mascot {
     year_of_birth: u32,
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<dyn Error>> {
     let ferris = Mascot {
         name: "Ferris".to_owned(),
         species: "crab".to_owned(),
         year_of_birth: 2015,
     };
 
-    let mut ferris_file = File::create("examples/ferris.cbor")?;
+    let ferris_file = File::create("examples/ferris.cbor")?;
     // Write Ferris to the given file.
     // Instead of a file you can use any type that implements `io::Write`
     // like a HTTP body, database connection etc.
-    serde_cbor::to_writer(&mut ferris_file, &ferris)?;
+    serde_cbor::to_writer(ferris_file, &ferris)?;
 
-    let mut tux_file = File::open("examples/tux.cbor")?;
+    let tux_file = File::open("examples/tux.cbor")?;
     // Load Tux from a file.
     // Serde CBOR performs roundtrip serialization meaning that
     // the data will not change in any way.
-    let tux: Mascot = serde_cbor::from_reader(&mut tux_file)?;
+    let tux: Mascot = serde_cbor::from_reader(tux_file)?;
 
     println!("{:?}", tux);
     // prints: Mascot { name: "Tux", species: "penguin", year_of_birth: 1996 }

examples/readme.rs

@@ -13,24 +13,24 @@ struct Mascot {
     year_of_birth: u32,
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<dyn Error>> {
     let ferris = Mascot {
         name: "Ferris".to_owned(),
         species: "crab".to_owned(),
         year_of_birth: 2015,
     };
 
-    let mut ferris_file = File::create("examples/ferris.cbor")?;
+    let ferris_file = File::create("examples/ferris.cbor")?;
     // Write Ferris to the given file.
     // Instead of a file you can use any type that implements `io::Write`
     // like a HTTP body, database connection etc.
-    serde_cbor::to_writer(&mut ferris_file, &ferris)?;
+    serde_cbor::to_writer(ferris_file, &ferris)?;
 
-    let mut tux_file = File::open("examples/tux.cbor")?;
+    let tux_file = File::open("examples/tux.cbor")?;
     // Load Tux from a file.
     // Serde CBOR performs roundtrip serialization meaning that
     // the data will not change in any way.
-    let tux: Mascot = serde_cbor::from_reader(&mut tux_file)?;
+    let tux: Mascot = serde_cbor::from_reader(tux_file)?;
 
     println!("{:?}", tux);
     // prints: Mascot { name: "Tux", species: "penguin", year_of_birth: 1996 }