Reduce severity of HasManyOrHasOneDependent rule

This is actually a hack. We want Hound to warn us about this rule;
however, we don't want to be notified about our many existing offenses.

Ideally we would add the `dependent` option to all existing models.
However, this is extra tricky because adding this option would change
existing behavior.

.rubocop.yml

@@ -1,3 +1 @@
 inherit_from: .rubocop_basic.yml
-Rails/HasManyOrHasOneDependent:
-  Enabled: true

.rubocop_basic.yml

@@ -218,6 +218,10 @@ Rails/FindBy:
 Rails/FindEach:
   Enabled: true
 
+Rails/HasManyOrHasOneDependent:
+  Enabled: true
+  Severity: refactor
+
 Rails/HttpPositionalArguments:
   Enabled: true