Check signature for history keeper in a different process

lib/commands/core.js

@@ -3,6 +3,7 @@
 const Core = module.exports;
 const Util = require("../common-util");
 const escapeKeyCharacters = Util.escapeKeyCharacters;
+const { fork } = require('child_process');
 
 /*  Use Nacl for checking signatures of messages */
 const Nacl = require("tweetnacl/nacl-fast");