Coverage 4.0 renames status.dat to status.json

The coverage publisher in the ShiningPanda plugin tries to determine if coverage has run with a few files in the output directory. Among them is status.dat. However, starting from version 4, coverage will generate its status file as status.json, which causes the coverage publisher to generate a warning about not finding the coverage output directory and fail the build.

Even though coverage 4.0a5 is still an alpha, this might not be the case for long.