update root readme

Author: nitishdayal

readme.md

@@ -25,7 +25,7 @@ The starter files include solutions to most challenges, so this isn't really mea
 1. [x] ~~[JavaScript Drum Kit](./exercises/01\ -\ JavaScript\ Drum\ Kit/)~~
 2. [x] ~~[JS + CSS Clock](./exercises/02\ -\ JS\ +\ CSS\ Clock/)~~
 3. [x] ~~[CSS Variables](./exercises/03\ -\ CSS\ Variables/)~~
-4. [ ] [Array Cardio, Day 1](./exercises/04\ -\ Array\ Cardio\ Day\ 1/)
+4. [x] ~~[Array Cardio, Day 1](./exercises/04\ -\ Array\ Cardio\ Day\ 1/)~~
 5. [ ] Flex Panel Gallery
 6. [ ] Type Ahead
 7. [ ] Array Cardio, Day 2