move to license-expression

Author: michalsta

pyproject.toml

@@ -10,7 +10,7 @@ name = "IsoSpecPy"
 dependencies = ["cffi"]
 description = "IsoSpecPy is a Python library for computing isotopic distributions of molecules."
 version = "2.3.0dev6"
-license = "BSD-2-Clause"
+license-expression = "BSD-2-Clause"
 license-files = ["LICENCE"]
 authors = [{name = "Michał Startek"}, {name = "Mateusz Łącki"}]
 readme = "README.md"