Fix links yet again so the linter is happy

Author: RealOrangeOne

_data/sidebar_tree.yaml

@@ -18,7 +18,7 @@ tree:
     - url: /kit/brain_board
       title: Brain Board
       tree:
-        - url: /kit/brain_board/updates/
+        - url: /kit/brain_board/updates
           title: Updates
     - url: /kit/motor_board
       title: Motor Board

kit/brain_board/index.md

@@ -24,7 +24,7 @@ The SD card is located on the underside of the board. Carefully open the Brain B
 
 To fully update your Brain Board's software, or refresh it if you think it's not working correctly, you can flash our SD card image onto the microSD card in your Brain Board.
 
-To update the SD card, you'll need to download our image from the [updates page](./updates/). The latest version is `{{ latest_version }}`.
+To update the SD card, you'll need to download our image from the [updates page]({{ site.baseurl }}/kit/brain_board/updates). The latest version is `{{ latest_version }}`.
 The flashing procedure is identical to flashing Raspberry Pi images.
 
 ## Etcher