chore: updated license information

Author: aj3sh

setup.cfg

@@ -1,7 +1,7 @@
 [metadata]
 name = commitlint
 version = attr: commitlint.__version__.__version__
-license = MIT
+license = GPL-3.0
 author = opensource-nepal
 author_email = aj3sshh@gmail.com, sugatbajracharya49@gmail.com
 description = commitlint is is a pre-commit hook designed to lint your commit messages according to the Conventional Commits standard.
@@ -19,6 +19,7 @@ keywords =
 classifiers =
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3.8
+    License :: OSI Approved :: GNU General Public License v3 (GPL-3.0)
 
 url = https://github.com/opensource-nepal/commitlint
 project_urls =