Update match-types.md

corrected syntax

Author: nmcb

docs/_docs/reference/new-types/match-types.md

@@ -83,7 +83,7 @@ following conditions are met:
    and these types are `=:=` to their corresponding type patterns in the match
    type
 
-So you know, While the case body will be expected to have the type on the right-hand
+So you know, while the case body will be expected to have the type on the right-hand
 side of the corresponding match type case, that doesn't imply the match type argument
 is constrained.  Using the example, the last case body must conform to X, but that
 doesn't constrain X to be AnyVal, and therefore a LeafElem[X] inside the body wouldn't