Fix format argument in JRuby

Logging from JRuby seems to have been subtly broken since the format
argument was [added for the C extension, but not for JRuby][commit].

One of the tests added in the previous commits triggered this.

[commit]: #921

lib/appsignal/extension/jruby.rb

@@ -80,7 +80,7 @@ def self.lib_extension
 
         # Logging methods
         attach_function :appsignal_log,
-          [:appsignal_string, :int32, :appsignal_string, :pointer],
+          [:appsignal_string, :int32, :int32, :appsignal_string, :pointer],
           :void
 
         # Transaction methods
@@ -273,10 +273,11 @@ def get_server_state(key)
         make_ruby_string state if state[:len] > 0
       end
 
-      def log(group, level, message, attributes)
+      def log(group, level, format, message, attributes)
         appsignal_log(
           make_appsignal_string(group),
           level,
+          format,
           make_appsignal_string(message),
           attributes.pointer
         )