method to_base64 add redundant quotations

[mahdi739]

Code to reproduce:

String::from_utf8(base64::engine::general_purpose::URL_SAFE_NO_PAD.decode("123".to_base64().unwrap() .as_ref()).unwrap()).unwrap();

Expected output:

123

Actual output:

"123"

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It works correctly with the inner method from_base64, I assume it's because of using serde_json::to_vec and serde_json::from_slice implicitly in to_base64 and from_base64.

I don't know if it does that on purpose and make sense for internal usage. But because it's a public API I think It'd be better to be usable from other crates.