Convert tests to use plain rspec-puppet

Tests in the new style produces the following documentation output:

abs
  should not eq nil
  should run abs() and raise an Puppet::ParseError
  should run abs(-34) and return 34
  should run abs("-34") and return 34
  should run abs(34) and return 34
  should run abs("34") and return 34

1 files changed, 1 insertions, 0 deletions

diff --git a/Gemfile b/Gemfile
index 9d38f35..e35a729 100644
--- a/Gemfile
+++ b/Gemfile
@@ -15,6 +15,7 @@ group :development, :unit_tests do
   gem 'rspec', '~> 3.1.0',       :require => false
   gem 'rspec-puppet',            :require => false
   gem 'mocha',                   :require => false
+  # keep for its rake task for now
   gem 'puppetlabs_spec_helper',  :require => false
   gem 'puppet-lint',             :require => false
   gem 'metadata-json-lint',      :require => false