book_changes is missing "validated": true field in JSON-RPC response

[mDuo13]

Issue Description

API methods that may return data from validated or unvalidated ledger versions are supposed to specify "validated": true when they pull data from a validated ledger version. The book_changes API method does this in the WebSocket version but not the JSON-RPC version for some reason.

Steps to Reproduce

Send a JSON-RPC request such as the following to a mainnet server:

{
    "method": "book_changes",
    "params": [{
      "ledger_index": 88377311
    }]
}

Expected Result

The response should have "validated": true in the result field.

Actual Result

There is no such field.

Environment

Tested on xrplcluster.com servers.

Clio servers (such as the ones in s1.ripple.com) do not seem to have this problem.