fix JSON::GeneratorError - source sequence is illegal/malformed utf-8:

[sahilchopra]

#30

[stuarthannig]

https://ruby-doc.org/core-2.3.0/Marshal.html#module-Marshal-label-Security+considerations

Security considerations¶ ↑

By design, ::load can deserialize almost any class loaded into the Ruby process. In many cases this can lead to remote code execution if the Marshal data is loaded from an untrusted source.

As a result, ::load is not suitable as a general purpose serialization format and you should never unmarshal user supplied input or other untrusted data.

If you need to deserialize untrusted data, use JSON or another serialization format that is only able to load simple, ‘primitive’ types such as String, Array, Hash, etc. Never allow user input to specify arbitrary types to deserialize into.