Use UTC in Rubocop todo file generation

Most of our team is distributed, so this is what the diff for our todo file
usually looks like:

```
- # on 2020-06-05 11:48:43 +1000 using RuboCop version 0.80.1.
+ # on 2020-06-12 12:23:47 -0300 using RuboCop version 0.80.1.
```

.rubocop_todo.yml

@@ -1,6 +1,6 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2020-05-23 16:26:03 +0200 using RuboCop version 0.84.0.
+# on 2020-06-12 17:42:47 UTC using RuboCop version 0.85.1.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
@@ -13,7 +13,7 @@ InternalAffairs/NodeDestructuring:
 # Offense count: 48
 # Configuration parameters: CountComments.
 Metrics/ClassLength:
-  Max: 190
+  Max: 186
 
 # Offense count: 198
 # Configuration parameters: CountComments, ExcludedMethods.
@@ -33,13 +33,13 @@ RSpec/AnyInstance:
     - 'spec/rubocop/cop/team_spec.rb'
     - 'spec/rubocop/target_finder_spec.rb'
 
-# Offense count: 972
+# Offense count: 981
 # Configuration parameters: Prefixes.
 # Prefixes: when, with, without
 RSpec/ContextWording:
   Enabled: false
 
-# Offense count: 3766
+# Offense count: 3810
 # Configuration parameters: Max.
 RSpec/ExampleLength:
   Enabled: false
@@ -58,7 +58,7 @@ RSpec/ExpectOutput:
     - 'spec/rubocop/result_cache_spec.rb'
     - 'spec/rubocop/target_finder_spec.rb'
 
-# Offense count: 430
+# Offense count: 434
 RSpec/MultipleExpectations:
   Max: 25
 

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#8111](https://github.com/rubocop-hq/rubocop/pull/8111): Add auto-correct for `Style/StructInheritance`. ([@tejasbubane][])
 * [#8113](https://github.com/rubocop-hq/rubocop/pull/8113): Let `expect_offense` templates add variable-length whitespace with `_{foo}`. ([@eugeneius][])
+* [#8146](https://github.com/rubocop-hq/rubocop/pull/8146): Use UTC in Rubocop todo file generation. ([@mauro-oto][])
 
 ### Bug fixes
 
@@ -4590,3 +4591,4 @@
 [@burnettk]: https://github.com/burnettk
 [@andrykonchin]: https://github.com/andrykonchin
 [@avrusanov]: https://github.com/avrusanov
+[@mauro-oto]: https://github.com/mauro-oto

lib/rubocop/formatter/disabled_config_formatter.rb

@@ -74,7 +74,7 @@ def command
       end
 
       def timestamp
-        @options[:no_auto_gen_timestamp] ? '' : "on #{Time.now} "
+        @options[:no_auto_gen_timestamp] ? '' : "on #{Time.now.utc} "
       end
 
       def output_offenses