Add test to JSON parser

[lmorg]

test: unit private murex-try {
    "StderrMatch": "bar\n",
    "StderrType":  "str",
}

Should detect tailing comma. eg: utils/mxjson/invalid_test.go

		{
			Json: `{
				"StderrMatch": "bar\n",
				"StderrType":  "str",
				}`,
			Error: true,
		},