Add a META.yml to the distribution. Your buildtool should be able to autogenerate it.
Fix MANIFEST.SKIP or use an authoring tool which respects MANIFEST.SKIP. Note that each entry in MANIFEST.SKIP is a regular expression. You may need to add appropriate meta characters not to ignore necessary stuff.
List all used modules in META.yml requires
Remove the POD errors. You can check for POD errors automatically by including Test::Pod to your test suite.
Error: Chemistry-Ring-0.11/lib/Chemistry/Ring.pm -- Around line 130: Non-ASCII character seen before =encoding in 'HÃ¼ckel's'. Assuming CP1252
Add a META.json to the distribution. Your buildtool should be able to autogenerate it.
Define the license if you are using in Build.PL. If you are using MakeMaker (Makefile.PL) you should upgrade to ExtUtils::MakeMaker version 6.31.
Add 'use warnings' (or its equivalents) to all modules, or convince us that your favorite module is well-known enough and people can easily see the modules warn when something bad happens.
List all modules used in the test suite in META.yml test_requires
This is not a critical issue. Currently mainly informative for the CPANTS authors. It might be removed later.