Update 4first-instruction-in-kernel2.rst

source/chapter1/4first-instruction-in-kernel2.rst

@@ -38,7 +38,7 @@
     #![no_std]
     #![no_main]
 
-    mod lang_item;
+    mod lang_items;
 
     use core::arch::global_asm;
     global_asm!(include_str!("entry.asm"));