Update pyproject.toml

Author: hexane360

pyproject.toml

@@ -8,21 +8,22 @@ version = "0.4"
 authors = [
   {name = "Colin Gilgenbach", email = "hexane@mit.edu"},
 ]
-license = {file = "LICENSE.txt"}
 description = "A modern, extensible library for creating atomic structures"
 readme = "README.md"
 keywords = ["science", "atoms", "materials", "chemistry"]
+license = "MPL-2.0"
+license-files = ["LICENSE.txt"]
 classifiers = [
     "Programming Language :: Python :: 3",
     "Programming Language :: Python :: 3 :: Only",
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
     "Development Status :: 4 - Beta",
     "Intended Audience :: Science/Research",
     "Topic :: Scientific/Engineering :: Physics",
-    "License :: OSI Approved :: Mozilla Public License 2.0 (MPL 2.0)",
     "Typing :: Typed",
 ]