CrateData: don't allocate String when Serialize, &str is enough

src/librustdoc/html/render/search_index.rs

@@ -299,7 +299,7 @@ fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
             )?;
             crate_data.serialize_field(
                 "p",
-                &self.paths.iter().map(|(it, s)| (it, s.to_string())).collect::<Vec<_>>(),
+                &self.paths.iter().map(|(it, s)| (it, s.as_str())).collect::<Vec<_>>(),
             )?;
             if has_aliases {
                 crate_data.serialize_field("a", &self.aliases)?;