Box ItemKind to reduce the size of `Item`

This brings the size of `Item` from

```
[src/librustdoc/lib.rs:103] std::mem::size_of::<Item>() = 680
```

to

```
[src/librustdoc/lib.rs:103] std::mem::size_of::<Item>() = 280
```

1 files changed, 1 insertions, 1 deletions

diff --git a/src/librustdoc/formats/renderer.rs b/src/librustdoc/formats/renderer.rs
index fbbd3c1ccf5..e84a9853d9b 100644
--- a/src/librustdoc/formats/renderer.rs
+++ b/src/librustdoc/formats/renderer.rs
@@ -89,7 +89,7 @@ crate fn run_format<'tcx, T: FormatRenderer<'tcx>>(
             }
 
             cx.mod_item_in(&item, &name, &cache)?;
-            let module = match item.kind {
+            let module = match *item.kind {
                 clean::StrippedItem(box clean::ModuleItem(m)) | clean::ModuleItem(m) => m,
                 _ => unreachable!(),
             };