Update requirements to match Puppet docs

.travis.yml

@@ -17,6 +17,8 @@ matrix:
       env: RUBOCOP_TEST="false" RSPEC_TEST="true" PUPPET_VERSIONS="4.10.10"
     - rvm: 2.2
       env: RUBOCOP_TEST="false" RSPEC_TEST="true" PUPPET_VERSIONS="4.10.10"
+    - rvm: 2.1
+      env: RUBOCOP_TEST="false" RSPEC_TEST="true" PUPPET_VERSIONS="4.10.10"
     # For really old ruby versions only build 3.8.7
     - rvm: 2.1
       env: RUBOCOP_TEST="false" RSPEC_TEST="true" PUPPET_VERSIONS="3.8.7"

doc/requirements.md

@@ -2,10 +2,14 @@
 
 To run `octocatalog-diff` you will need these basics:
 
-- Ruby 2.0 through 2.4 (we test octocatalog-diff with Ruby 2.0, 2.1, 2.2, 2.3, and 2.4)
+- An appropriate Puppet version and [corresponding ruby version](https://puppet.com/docs/puppet/5.4/system_requirements.html)
+  - Puppet 5.x officially supports Ruby 2.4
+  - Puppet 4.x officially supports Ruby 2.1, but seems to work fine with later versions as well
+  - Puppet 3.8.7 -- we attempt to maintain compatibility in `octocatalog-diff` to facilitate upgrades even though this version is no longer supported by Puppet
+  - We don't officially support Puppet 3.8.6 or before
 - Mac OS, Linux, or other Unix-line operating system (Windows is not supported)
 - Ability to install gems, e.g. with [rbenv](https://github.com/rbenv/rbenv) or [rvm](https://rvm.io/), or root privileges to install into the system Ruby
-- Puppet agent for [Linux](https://docs.puppet.com/puppet/latest/reference/install_linux.html) or [Mac OS X](https://docs.puppet.com/puppet/latest/reference/install_osx.html), or installed as a gem (we support Puppet 3.8.7 and all versions of Puppet 4.x)
+- Puppet agent for [Linux](https://docs.puppet.com/puppet/latest/reference/install_linux.html) or [Mac OS X](https://docs.puppet.com/puppet/latest/reference/install_osx.html), or installed as a gem
 
 We recommend that you also have the following to get the most out of `octocatalog-diff`, but these are not absolute requirements: