0.7.0 in crates.io is not using pyo3==0.20

[sun-rs]

There seems to be a conflict on 0.7.0 with pyo3=0.20.

error: failed to select a version for `pyo3-ffi`.
    ... required by package `pyo3 v0.19.0`
    ... which satisfies dependency `pyo3 = "^0.19.0"` of package `pyo3-polars v0.7.0`
    ... which satisfies dependency `pyo3-polars = "^0.7.0"` of package `valar v0.37.4 (D:\SUN\valar)`
versions that meet the requirements `=0.19.0` are: 0.19.0

the package `pyo3-ffi` links to the native library `python`, but it conflicts with a previous package which links to `python` as well:
package `pyo3-ffi v0.20.0`
    ... which satisfies dependency `pyo3-ffi = "=0.20.0"` of package `pyo3 v0.20.0`
    ... which satisfies dependency `pyo3 = "^0.20"` of package `valar v0.37.4 (D:\SUN\valar)`
Only one package in the dependency graph may specify the same links value. This helps ensure that only one copy of a native library is linked in the final binary. Try to adjust your dependencies so that only one package uses the links ='pyo3-ffi' value. For more information, see https://doc.rust-lang.org/cargo/reference/resolver.html#links.

failed to select a version for `pyo3-ffi` which could resolve this conflict

[aldanor]

@sun-rs Can be closed; see comments here: #35