Fix json produced by /profiler/realtime when there is a double quotation mark in a command.

After a request containing double quotation mark is done, the profiler cannot produce valid json because the quotation mark is not escaped in json keys.

Extract of invalid produced json:
```,"db.project.command.sql.select from User where name = "jeremy"":```

I also suggest to use a library to generate json, to avoid this kind of problem.