Install `prometheus` when finding a newer version.

cookbooks/prometheus/install.rb

@@ -1,6 +1,9 @@
 prometheus_url = ''
 prometheus_bin = ''
 
+vtag           = ''
+tag            = ''
+
 # Calculate the Download URL:
 begin
   require 'net/http'
@@ -22,6 +25,10 @@ rescue
   raise 'Cannot connect to http://github.com.'
 end
 
+
+# バージョン確認して、アップデート必要かどうか確認
+result = run_command("prometheus --version 2>&1 | grep #{tag}", error: false)
+if result.exit_status != 0
   # Download:
   TMP = "/tmp/#{prometheus_bin}"
 
@@ -47,3 +54,4 @@ end
   link "#{node['prometheus']['location']}prometheus" do
     to "#{node['prometheus']['storage']}prometheus"
   end
+end