feat(clippy): Use clippy for it's extra lints

serde_tests/tests/test.rs

@@ -1,3 +1,6 @@
+#![cfg_attr(feature = "nightly", feature(plugin))]
+#![cfg_attr(feature = "nightly", plugin(clippy))]
+
 extern crate num;
 extern crate serde;
 

serde_tests/tests/test_de.rs

@@ -95,12 +95,12 @@ declare_tests! {
     test_char {
         'a' => vec![Token::Char('a')],
         'a' => vec![Token::Str("a")],
-        'a' => vec![Token::String("a".to_string())],
+        'a' => vec![Token::String("a".to_owned())],
     }
     test_string {
-        "abc".to_string() => vec![Token::Str("abc")],
-        "abc".to_string() => vec![Token::String("abc".to_string())],
-        "a".to_string() => vec![Token::Char('a')],
+        "abc".to_owned() => vec![Token::Str("abc")],
+        "abc".to_owned() => vec![Token::String("abc".to_owned())],
+        "a".to_owned() => vec![Token::Char('a')],
     }
     test_option {
         None::<i32> => vec![Token::Unit],

serde_tests/tests/test_ser.rs

@@ -63,7 +63,7 @@ declare_ser_tests! {
     }
     test_str {
         "abc" => &[Token::Str("abc")],
-        "abc".to_string() => &[Token::Str("abc")],
+        "abc".to_owned() => &[Token::Str("abc")],
     }
     test_option {
         None::<i32> => &[Token::Option(false)],

serde_tests/tests/token.rs

@@ -325,7 +325,7 @@ impl de::Error for Error {
     fn end_of_stream() -> Error { Error::EndOfStreamError }
 
     fn unknown_field(field: &str) -> Error {
-        Error::UnknownFieldError(field.to_string())
+        Error::UnknownFieldError(field.to_owned())
     }
 
     fn missing_field(field: &'static str) -> Error {