fix SciPy DeprecationWarning

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (57c5004) 82.96% compared to head (fb685d0) 82.96%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #551 +/- ## ======================================= Coverage 82.96% 82.96% ======================================= Files 73 73 Lines 6510 6510 ======================================= Hits 5401 5401 Misses 1109 1109 ``` | [Files](https://app.codecov.io/gh/deepmodeling/dpdata/pull/551?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepmodeling) | Coverage Δ | | |---|---|---| | [dpdata/amber/md.py](https://app.codecov.io/gh/deepmodeling/dpdata/pull/551?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepmodeling#diff-ZHBkYXRhL2FtYmVyL21kLnB5) | `97.53% <100.00%> (ø)` | |

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