Fix a build error

This PR fixes the following build error:

```console
$ bundle exec rake
(snip)

Offenses:

lib/rubocop/cop/rails/reversible_migration.rb:310:46: C: [Correctable] InternalAffairs/RedundantMethodDispatchNode:
Remove the redundant send_node.
            (ancestor.block_type? && ancestor.send_node.method?(:reversible)) || ancestor.send_node.method?(:up_only)
                                             ^^^^^^^^^^
lib/rubocop/cop/rails/reversible_migration.rb:310:90: C: [Correctable] InternalAffairs/RedundantMethodDispatchNode:
Remove the redundant send_node.
            (ancestor.block_type? && ancestor.send_node.method?(:reversible)) || ancestor.send_node.method?(:up_only)
                                                                                         ^^^^^^^^^^

285 files inspected, 2 offenses detected, 2 offenses autocorrectable
```

Author: koic

lib/rubocop/cop/rails/reversible_migration.rb

@@ -307,7 +307,7 @@ def within_change_method?(node)
 
         def within_reversible_or_up_only_block?(node)
           node.each_ancestor(:block).any? do |ancestor|
-            (ancestor.block_type? && ancestor.send_node.method?(:reversible)) || ancestor.send_node.method?(:up_only)
+            (ancestor.block_type? && ancestor.method?(:reversible)) || ancestor.method?(:up_only)
           end
         end