update version to include revision & channel

lib/postal/http.rb

@@ -42,7 +42,7 @@ module Postal
         #request.add_field 'X-Postal-Signature', signature
       end
 
-      request['User-Agent'] = options[:user_agent] || "Postal/#{Postal::VERSION}"
+      request['User-Agent'] = options[:user_agent] || "Postal/#{Postal.version}"
 
       connection = Net::HTTP.new(uri.host, uri.port)
 

lib/postal/version.rb

@@ -1,3 +1,11 @@
 module Postal
+
   VERSION = '1.0.0'
+  REVISION = nil
+  CHANNEL = 'dev'
+
+  def self.version
+    [VERSION, REVISION, CHANNEL].compact.join('-')
+  end
+
 end