Install Ruby in the backup cookbook

Also switch to the 5.0 beta version, it works with modern Rubies

site-cookbooks/backup/recipes/default.rb

@@ -23,8 +23,12 @@
 # OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
+build_essential 'backup gem'
+
+package ["ruby", "ruby-dev"]
+
 gem_package 'backup' do
-  version '4.4.0'
+  version '5.0.0.beta.2'
 end
 
 backup_data = Chef::EncryptedDataBagItem.load('credentials', 'backup')