cookie -> mvt

Author: Jakeii

dotcom-rendering/docs/development/ab-testing-in-dcr.md

@@ -68,9 +68,9 @@ Server side tests are also available in the CAPI object e.g. `CAPIArticle.config
 
 Use the opt-in and opt-out URL fragments to force yourself into or out of a test.
 
-When opted-in, the test will override any cookie based assignment and you'll only be in the specified test group.
+When opted-in, the test will override any mvt based assignment and you'll only be in the opted-in test group.
 
-When opted-out, you'll return to random/cookie based assignment.
+When opted-out, you'll return to random/mvt based assignment.
 
 These links are also in the [frontend admin](https://frontend.gutools.co.uk/analytics/ab-testing).