gems: update rack-tracer to version 0.8.0

Since rack-tracer now supports OpenTracing.active_span we should start
using it as well and therefore do not need spanmanager gem anymore.

See: Update rack-tracer to version 0.8.0 (#16)

dyndnsd.gemspec

@@ -24,8 +24,7 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency 'json'
   s.add_runtime_dependency 'metriks'
   s.add_runtime_dependency 'opentracing', '~> 0.4.0'
-  s.add_runtime_dependency 'rack-tracer', '~> 0.6.0'
-  s.add_runtime_dependency 'spanmanager', '~> 0.3.0'
+  s.add_runtime_dependency 'rack-tracer', '~> 0.8.0'
   s.add_runtime_dependency 'jaeger-client', '~> 0.6.0'
 
   s.add_development_dependency 'bundler'

lib/dyndnsd.rb

@@ -10,7 +10,6 @@ require 'metriks'
 require 'metriks/reporter/graphite'
 require 'opentracing'
 require 'rack/tracer'
-require 'spanmanager'
 
 require 'dyndnsd/generator/bind'
 require 'dyndnsd/updater/command_with_bind_zone'
@@ -266,8 +265,6 @@ module Dyndnsd
           host: host, port: port, service_name: service_name, flush_interval: 1
         )
       end
-      # always use SpanManager
-      OpenTracing.global_tracer = SpanManager::Tracer.new(OpenTracing.global_tracer)
     end
 
     private_class_method def self.setup_rack(config)

lib/dyndnsd/helper.rb

@@ -28,13 +28,14 @@ module Dyndnsd
     end
 
     def self.span(operation, &block)
-      span = OpenTracing.start_span(operation)
+      scope = OpenTracing.start_active_span(operation)
+      span = scope.span
       span.set_tag('component', 'dyndnsd')
       span.set_tag('span.kind', 'server')
       begin
         block.call(span)
       ensure
-        span.finish
+        scope.close
       end
     end
   end