Update license references from GPL to MIT

Author: atpage

README.md

@@ -88,7 +88,7 @@ The module is also to some extent described in my tutorial series:
 
 
 ## License
-The module is licensed under the [GNU General Public License Version3, GPL-v3](https://opensource.org/licenses/GPL-3.0)
+The module is licensed under the [MIT License](https://opensource.org/licenses/MIT)
 
 ## Validation
 Initial results of the validation have been reported in [1, 2].

setup.py

@@ -44,7 +44,7 @@
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
-        "License :: OSI Approved :: GNU General Public License (GPL)",
+        "License :: OSI Approved :: MIT License",
         "Operating System :: OS Independent",
     ],
 )