Fix an invalid example of JSON report in advanced.md
Fix an invalid example of JSON report in advanced.md

This is just a mistake in the document. Google Test doesn't output
such an invalid JSON report.

Signed-off-by: Keiichi Watanabe <815e4e8f7c92a23424d7c3f51ead622bcedbc720@chromium.org>

gianricardo/googletest,jlanecox/googletest,google/googletest,xnagireddy/googletest,google/googletest,antidotcb/googletest,antidotcb/googletest,empiredan/googletest,google/googletest,xnagireddy/googletest,xnagireddy/googletest,jlanecox/googletest,antidotcb/googletest,jlanecox/googletest,gianricardo/googletest,antidotcb/googletest,jlanecox/googletest,empiredan/googletest,google/googletest,xnagireddy/googletest,gianricardo/googletest,empiredan/googletest