chore: update license references

Author: Sam Harrison

MANIFEST.in

@@ -1,3 +1,3 @@
-include LICENSE.txt VERSION.txt README.rst
+include LICENSE VERSION.txt README.rst
 recursive-include python_http_client *.py *.txt
 prune tests

README.rst

@@ -154,7 +154,7 @@ License
 .. _CHANGELOG: https://github.com/sendgrid/python-http-client/blob/HEAD/CHANGELOG.md
 .. _birdy: https://github.com/inueni/birdy
 .. _universalclient: https://github.com/dgreisen/universalclient
-.. _The MIT License (MIT): https://github.com/sendgrid/python-http-client/blob/HEAD/LICENSE.md
+.. _The MIT License (MIT): https://github.com/sendgrid/python-http-client/blob/HEAD/LICENSE
 .. _this is an incredible opportunity to join our #DX team: https://sendgrid.com/careers/role/1421152/?gh_jid=1421152
 
 .. |Build Status| image:: https://travis-ci.org/sendgrid/python-http-client.svg?branch=main
@@ -174,4 +174,4 @@ License
 .. |GitHub contributors| image:: https://img.shields.io/github/contributors/sendgrid/python-http-client.svg
    :target: https://github.com/sendgrid/python-http-client/graphs/contributors
 .. |MIT licensed| image:: https://img.shields.io/badge/license-MIT-blue.svg
-   :target: https://github.com/sendgrid/python-http-client/blob/HEAD/LICENSE.md
+   :target: https://github.com/sendgrid/python-http-client/blob/HEAD/LICENSE

tests/test_daterange.py

@@ -8,7 +8,7 @@ class DateRangeTest(unittest.TestCase):
     def setUp(self):
         self.openlicensefile = os.path.join(
                                 os.path.dirname(__file__),
-                                '../LICENSE.md')
+                                '../LICENSE')
         self.pattern = 'Copyright (C) %s, Twilio SendGrid, Inc.' % (
                         time.strftime("%Y"))
         fh = open(self.openlicensefile)

tests/test_repofiles.py

@@ -14,7 +14,7 @@ class RepoFiles(unittest.TestCase):
         ['./CODE_OF_CONDUCT.md'],
         ['./CONTRIBUTING.md'],
         ['./ISSUE_TEMPLATE.md'],
-        ['./LICENSE.md', './LICENSE.txt'],
+        ['./LICENSE'],
         ['./PULL_REQUEST_TEMPLATE.md'],
         ['./README.rst'],
         ['./TROUBLESHOOTING.md'],