Escape exception message in JSON Printer

When the JSON printer needs to handle an exception, but the exception contains quotation marks, it creates an illegal JSON format. This can easily be fixed by escaping the exception message here: https://github.com/Guardsquare/proguard-core/blob/master/base/src/main/java/proguard/evaluation/util/jsonprinter/ErrorRecord.java#L47. A breaking example is the "Changing stack size" test.