refs.h: HEAD is not that special

In-code comment explains pseudorefs but used a wrong nomenclature
"special ref".

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

refs.h

@@ -56,7 +56,7 @@ struct worktree;
  * Even with RESOLVE_REF_ALLOW_BAD_NAME, names that escape the refs/
  * directory and do not consist of all caps and underscores cannot be
  * resolved. The function returns NULL for such ref names.
- * Caps and underscores refers to the special refs, such as HEAD,
+ * Caps and underscores refers to the pseudorefs, such as HEAD,
  * FETCH_HEAD and friends, that all live outside of the refs/ directory.
  */
 #define RESOLVE_REF_READING 0x01