Update design-document.md

One typo :)

accepted/future-releases/3009-inference-using-bounds/design-document.md

@@ -352,7 +352,7 @@ constraints collected during the upwards phase (1), a new constraint (2) is
 generated from the bound of the type variable after completing the first four
 steps of the CSSTV algorithm. The new constraint is then added to the set of
 existing constraints (1). Then the solution for the type variable is computed
-form the updated constraint set (3).
+from the updated constraint set (3).
 
 ```mermaid
 block-beta