Merge pull request swiftlang#40984 from tshortli/python-lint-python3

Utils: Update python linter to specify python3 installation of flake8

Author: tshortli

utils/python_lint.py

@@ -45,8 +45,8 @@
 
 You can install these using:
 
-    python -m pip install flake8
-    python -m pip install flake8-import-order
+    python3 -m pip install flake8
+    python3 -m pip install flake8-import-order
 
 For more help, see http://flake8.pycqa.org.
 """