use deep_copy in CombinePolicies just in case

Author: oreoshake

lib/secure_headers/headers/policy_management.rb

@@ -218,7 +218,7 @@ def combine_policies(original, additions)
           raise ContentSecurityPolicyConfigError.new("Attempted to override an opt-out CSP config.")
         end
 
-        original = original.dup
+        original = Configuration.send(:deep_copy, original)
         populate_fetch_source_with_default!(original, additions)
         merge_policy_additions(original, additions)
       end