Exclude migrations from Style/MutableConstant

.rubocop.yml

...evelopers_can_merge_to_protected_branches_merge_access.rb

..._developers_can_push_to_protected_branches_push_access.rb

...igrate/20160729173930_remove_project_id_from_spam_logs.rb

db/migrate/20160823081327_change_merge_error_to_text.rb

db/migrate/20160824124900_add_table_issue_metrics.rb

db/migrate/20160825052008_add_table_merge_request_metrics.rb

...e/20160831223750_remove_features_enabled_from_projects.rb

db/migrate/20160913162434_remove_projects_pushes_since_gc.rb

db/migrate/20160913212128_change_artifacts_size_column.rb

...te/20160915042921_create_merge_requests_closing_issues.rb

db/migrate/20160919144305_add_type_to_labels.rb

db/migrate/20161014173530_create_label_priorities.rb

db/migrate/20161017125927_add_unique_index_to_labels.rb

db/migrate/20161018024215_migrate_labels_priority.rb

db/migrate/20161018024550_remove_priority_from_labels.rb

...ate/20161019190736_migrate_sidekiq_queues_from_default.rb

...e/20161019213545_generate_project_feature_for_projects.rb

...0161020083353_add_pipeline_id_to_merge_request_metrics.rb

...ate/20161024042317_migrate_mailroom_queue_from_default.rb