Merge pull request #1347 from elchukc/fix_typo_start_return_type

add return type on `_start()` in code block

blog/content/edition-2/posts/03-vga-text-buffer/index.md

@@ -656,7 +656,7 @@ Now we can use `println` in our `_start` function:
 // in src/main.rs
 
 #[no_mangle]
-pub extern "C" fn _start() {
+pub extern "C" fn _start() -> ! {
     println!("Hello World{}", "!");
 
     loop {}