Renaming a struct initializer to match the field name should use shorthand record syntax

[jyn514]

I have code like this:

let inner = unimplemented!();
Item { kind: inner, ..unimplemented!() }

When I rename inner to kind, I expect this to turn into Item { kind, ..unimplemented!() }.
Instead, it turns into Item { kind: kind, ..unimplemented!() }, and I have to hit ctrl+. again to get the short-hand syntax.