Fix broken link.

Author: peterhinch

v3/docs/DRIVERS.md

@@ -1018,7 +1018,7 @@ def add_item(q, data):
 ```
 ###### [Contents](./DRIVERS.md#0-contents)
 
-## 3.8 Delay_ms class
+# 8. Delay_ms class
 
 This implements the software equivalent of a retriggerable monostable or a
 watchdog timer. It has an internal boolean `running` state. When instantiated

v3/docs/TUTORIAL.md

@@ -1269,7 +1269,7 @@ watchdog timer. On timeout it can launch a callback or coroutine. It exposes an
 altered dynamically.
 
 It may be found in the `primitives` directory and is documented in
-[Delay_ms class](./DRIVERS.md#8-delay_ms class).
+[Delay_ms class](./DRIVERS.md#8-delay_ms-class).
 
 ## 3.9 Message