Difference between HalfCheetah-v1 and HalfCheetah-v2?

What is the difference between HalfCheetah-v1 and HalfCheetah-v2?
Can we compare results from tasks performed by these two? or are they very different?

[christopherhesse]

Looks like this was due to upgrading mujoco_py: From the README:

2018-01-24: All continuous control environments now use mujoco_py >= 1.50. Versions have been updated accordingly to -v2, e.g. HalfCheetah-v2. Performance should be similar (see #834) but there are likely some differences due to changes in MuJoCo.