[clangd] Fix a typo, NFC.

Author: hokein

clang-tools-extra/clangd/ClangdServer.h

@@ -274,7 +274,7 @@ class ClangdServer {
 
   /// Test the validity of a rename operation.
   ///
-  /// If NewName is provided, it peforms a name validation.
+  /// If NewName is provided, it performs a name validation.
   void prepareRename(PathRef File, Position Pos,
                      llvm::Optional<std::string> NewName,
                      const RenameOptions &RenameOpts,