Fix #23 - update supported versions (#25)

As of today, the supported versions are 9.3-9.6 and 10.5 
Tests for the regex: http://rubular.com/r/dwLli41ugF

Author: pmav99

controls/postgres_spec.rb

@@ -115,7 +115,7 @@
   title 'Use stable postgresql version'
   desc 'Use only community or commercially supported version of the PostgreSQL software. Do not use RC, DEVEL oder BETA versions in a production environment.'
   describe command('psql -V') do
-    its('stdout') { should match(/9.[1-5]/) }
+    its('stdout') { should match(/\b9\.[3-6]$|\b10\.5$/) }
   end
   describe command('psql -V') do
     its('stdout') { should_not match(/RC/) }