Update CHANGELOG.md

Fix DF calculation in DDP to make it more generic for variable length stages

CHANGELOG.md

@@ -65,7 +65,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed outputting capital recovery cost to 0 if the remaining number of years is 0 (#666)
 - Updated the docstring for the initialize_cost_to_go function and adjusted the formula for the discount factor to reflect the code implementation (#672).
 - Fix write_multi_stage_cost.jl: add discount with OPEX multipliers to cUnmetPolicyPenalty (#679)
-
+- Fix DF calculation in DDP to make it more generic for variable length stages
 ### Changed
 - Use add_to_expression! instead of the += and -= operators for memory performance improvements (#498).
 - Generally, 'demand' is now used where (electrical) 'load' was used previously (#397).