fix the implied_bounds_entailment lint

Author: lcnr

src/serialize.rs

@@ -1152,7 +1152,7 @@ impl<'a, T: ?Sized> Decodable for Cow<'a, T>
     where T: ToOwned, T::Owned: Decodable
 {
     #[inline]
-    fn decode<D: Decoder>(d: &mut D) -> Result<Cow<'static, T>, D::Error> {
+    fn decode<D: Decoder>(d: &mut D) -> Result<Cow<'a, T>, D::Error> {
         Ok(Cow::Owned(try!(Decodable::decode(d))))
     }
 }