Fix typo in stacks.mdoc

Author: dcousens

design-system/pkg/src/layout/docs/stacks.mdoc

@@ -29,7 +29,7 @@ The `VStack` is a thin wrapper around the `Flex` component, where the `direction
 </Flex>
 ```
 
-### Horiztonal stack
+### Horizontal stack
 
 The `HStack` is a thin wrapper around the `Flex` component, where the `direction` prop is set to `"row"`.
 
@@ -39,4 +39,4 @@ The `HStack` is a thin wrapper around the `Flex` component, where the `direction
   <Placeholder width="element.large" />
   <Placeholder width="element.large" />
 </Flex>
-```
+```