ToJson produces invalid json when input has smart quote characters

[twaddell]

Describe the bug
When processing a string containing curly quote characters they are converted to straight quotes which produces invalid Json when the ToJson Method is called

To Reproduce

Catalyst.Models.English.Register(); 

Storage.Current = new DiskStorage("catalyst-models");
var nlp = await Pipeline.ForAsync(Language.English);
var doc = new Document("The \u201cquick\u201d brown fox jumps over the lazy dog", Language.English);
nlp.ProcessSingle(doc);
Console.WriteLine(doc.ToJson());

This outputs the following to the console:

{"Language":"en","Length":45,"Value":"The "quick" brown fox jumps over the lazy dog","TokensData":[[{"Bounds":[0,2],"Tag":"DET"},{"Bounds":[4,4],"Tag":"PUNCT"},{"Bounds":[5,9],"Tag":"ADJ"},{"Bounds":[10,10],"Tag":"PUNCT"},{"Bounds":[12,16],"Tag":"ADJ"},{"Bounds":[18,20],"Tag":"NOUN"},{"Bounds":[22,26],"Tag":"VERB"},{"Bounds":[28,31],"Tag":"ADP"},{"Bounds":[33,35],"Tag":"DET"},{"Bounds":[37,40],"Tag":"ADJ"},{"Bounds":[42,44],"Tag":"NOUN"}]]}

Note the straight quotes around the word quick. This json cannot be parsed.

Expected behavior
The ToJson method should retain the unicode curly quotes in the Value property and produce valid json output.

[theolivenbaum]

Strange, as it seems like the code is using the right method to create the Json output.

Is this maybe just an issue with the console output replacing the escaped value back with the unescaped one? Does the same thing happen if you try to write the json output to a file?