fix escaping double quotes in toJSON method

[epanoff]

I have error in tomcat jmx output from my tomcat server. It is not valid json, because that have not esacaped double quotes.

example output: {"mBeanName" : "Catalina:type=RequestProcessor,worker=\"http-bio-8080\",name=HttpRequest37", "attribute" : "rpName", "attributeType" : "ObjectName", "value" : "Catalina:type=RequestProcessor,worker="http-bio-8080",name=HttpRequest37"}