mask format for winston

[kenglxn]

testet lokalt:

log.info(`Frackend startup: ${JSON.stringify({ NAIS_CLUSTER_NAME, MILJO, GIT_COMMIT })} 123123123`);

===>

{"level":"info","message":"Frackend startup: {\"NAIS_CLUSTER_NAME\":\"local\",\"MILJO\":\"local\",\"GIT_COMMIT\":\"?\"} *********"}
{"level":"info","message":"main started"}
{"level":"info","message":"Server listening on port 8080"}