Fix some dead links (pypa#148)

Co-authored-by: Dustin Ingram <[email protected]>

Author: marcelm

setup.py

@@ -36,7 +36,7 @@
     #
     # For a discussion on single-sourcing the version across setup.py and the
     # project code, see
-    # https://packaging.python.org/en/latest/single_source_version.html
+    # https://packaging.python.org/guides/single-sourcing-package-version/
     version='2.0.0',  # Required
 
     # This is a one-line description or tagline of what your project does. This
@@ -143,7 +143,7 @@
     # installed, so they must be valid existing projects.
     #
     # For an analysis of "install_requires" vs pip's requirements files see:
-    # https://packaging.python.org/discussions/install-requires-vs-requirements
+    # https://packaging.python.org/discussions/install-requires-vs-requirements/
     install_requires=['peppercorn'],  # Optional
 
     # List additional groups of dependencies here (e.g. development