Use &str instread of Option<String>

crates/ra_ide_api/src/display.rs

@@ -78,7 +78,7 @@ where
 pub(crate) fn doc_text_for(nav: NavigationTarget) -> Option<String> {
     match (nav.description(), nav.docs()) {
         (Some(desc), docs) => Some(rust_code_markup_with_doc(desc, docs)),
-        (None, Some(docs)) => Some(docs),
+        (None, Some(docs)) => Some(docs.to_string()),
         _ => None,
     }
 }