Fix case in links from Chapter 3 to .move files (MystenLabs#2579)

doc/src/build/programming-with-objects/ch3-immutable-objects.md

@@ -14,7 +14,7 @@ public native fun freeze_object<T: key>(obj: T);
 ```
 After this call, the specified object will become permanently immutable. This is a non-reversible operation; hence, freeze an object only when you are certain that it will never need to be mutated.
 
-Let's add an entry function to the [ColorObject](https://github.com/MystenLabs/sui/blob/main/sui_programmability/examples/objects_tutorial/sources/ColorObject.move) module to turn an existing (owned) `ColorObject` into an immutable object:
+Let's add an entry function to the [ColorObject](https://github.com/MystenLabs/sui/blob/main/sui_programmability/examples/objects_tutorial/sources/color_object.move) module to turn an existing (owned) `ColorObject` into an immutable object:
 ```rust
 public entry fun freeze_object(object: ColorObject) {
     transfer::freeze_object(object)