Update docs/_docs/reference/experimental/explicit-nulls.md

Co-authored-by: Ondřej Lhoták <[email protected]>

docs/_docs/reference/experimental/explicit-nulls.md

@@ -314,7 +314,7 @@ We illustrate the rules with following examples:
     "io.reactivex.annotations.NonNull" :: Nil map PreNamedString)
   ```
 
-The flexible types can be disabled by using `-Yno-flexible-types` flag.
+Flexible types can be disabled by using `-Yno-flexible-types` flag.
 The ordinary union type `| Null` will be used instead.
 
 ### Override check