v2.7.0: Added support for n-step returns for off-policy algorithms

Breaking Changes

• Upgraded to SB3 >= 2.7.0

New features

• Add n-step returns support with n_steps parameter

Bug fixes

• Use the FloatSchedule and LinearSchedule classes instead of lambdas in the ARS, PPO, and QRDQN implementations to improve model portability across different operating systems

New Contributors

• @akanto made their first contribution in #294

Full Changelog: v2.6.0...v2.7.0