Ruby231 (#155)

* Include puppet version requirements in metadata

* Support Ruby 2.3.1

This patch is needed to support the new Puppet v4 AIO which uses Ruby
2.3.1.

.travis.yml

@@ -21,6 +21,8 @@ matrix:
     env: PUPPET_GEM_VERSION="~> 3.0" FUTURE_PARSER="yes"
   - rvm: 2.1.9
     env: PUPPET_GEM_VERSION="~> 4.5.0"
+  - rvm: 2.3.1
+    env: PUPPET_GEM_VERSION="~> 4"
   - rvm: default
     sudo: required
     dist: trusty

metadata.json

@@ -8,6 +8,9 @@
   "project_page": "https://github.com/camptocamp/puppet-postfix",
   "issues_url": "https://github.com/camptocamp/puppet-postfix/issues",
   "description": "Postfix Module for Puppet",
+  "requirements": [
+    {"name":"puppet","version_requirement":">= 3.0.0 < 5.0.0" }
+  ],
   "dependencies": [
     {
       "name": "puppetlabs/stdlib",