Fix license formatting in pyproject.toml

Author: skirpichev

pyproject.toml

@@ -7,7 +7,8 @@ name = "python-gmp"
 dynamic = ["version"]
 description = "Safe bindings to the GNU GMP library"
 keywords = ["gmp", "multiple-precision", "arbitrary-precision", "bignum"]
-license = {text = "MIT"}
+license = "MIT"
+license-files = ["LICENSE"]
 authors = [{name = "Sergey B Kirpichev", email = "skirpichev@gmail.com"}]
 maintainers = [{name = "Sergey B Kirpichev", email = "skirpichev@gmail.com"}]
 classifiers = ["Development Status :: 3 - Alpha",