fix: clippy warning of rust 1.8.4 (#14984)

# Description

I'm on rust toolchain 1.8.4, and I can see clippy warnings that can't be
caught by the ci workflow, primarily related to lifetime params.

I think it doesn't hurt to fix those in advance.

# User-Facing Changes

# Tests + Formatting

# After Submitting

crates/nu-json/src/value.rs

@@ -432,7 +432,7 @@ struct WriterFormatter<'a, 'b: 'a> {
     inner: &'a mut fmt::Formatter<'b>,
 }
 
-impl<'a, 'b> io::Write for WriterFormatter<'a, 'b> {
+impl io::Write for WriterFormatter<'_, '_> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         fn io_error<E>(_: E) -> io::Error {
             // Value does not matter because fmt::Debug and fmt::Display impls