Address suggestions

Signed-off-by: Marco Costa <marco.costa@datadoghq.com>

lib/datadog/tracing/contrib/rails/runner.rb

@@ -4,10 +4,6 @@ module Datadog
   module Tracing
     module Contrib
       module Rails
-        # Limit the maximum size of the source code captured in the source tag.
-        MAX_TAG_VALUE_SIZE = 4096
-        private_constant :MAX_TAG_VALUE_SIZE
-
         # Instruments the `bin/rails runner` command.
         # This command executes the provided code with the host Rails application loaded.
         # The command can be either:
@@ -16,6 +12,10 @@ module Rails
         # * `inline code`: for code provided directly as a command line argument.
         # @see https://guides.rubyonrails.org/v6.1/command_line.html#bin-rails-runner
         module Runner
+          # Limit the maximum size of the source code captured in the source tag.
+          MAX_TAG_VALUE_SIZE = 4096
+          private_constant :MAX_TAG_VALUE_SIZE
+
           def runner(code_or_file = nil, *_command_argv)
             if code_or_file == '-'
               name = Ext::SPAN_RUNNER_STDIN

spec/datadog/tracing/contrib/rails/support/base.rb

@@ -1,6 +1,4 @@
 require 'rails/all'
-# Loaded by the `bin/rails` script in a real Rails application
-require 'rails/command' if Rails::VERSION::MAJOR > 4
 
 require_relative 'controllers'
 require_relative 'models'

spec/datadog/tracing/contrib/rails/support/rails5.rb

@@ -1,4 +1,6 @@
 require 'rails/all'
+# Loaded by the `bin/rails` script in a real Rails application
+require 'rails/command'
 
 if ENV['USE_SIDEKIQ']
   require 'sidekiq/testing'

spec/datadog/tracing/contrib/rails/support/rails6.rb

@@ -1,4 +1,6 @@
 require 'rails/all'
+# Loaded by the `bin/rails` script in a real Rails application
+require 'rails/command'
 
 if ENV['USE_SIDEKIQ']
   require 'sidekiq/testing'