log.SetReportCaller(true)
This adds the caller as 'method' like so:
{"animal":"penguin","level":"fatal","method":"github.com/sirupsen/arcticcreatures.migrate","msg":"a penguin swims by",
"time":"2014-03-10 19:57:38.562543129 -0400 EDT"}
time="2015-03-26T01:27:38-04:00" level=fatal method=github.com/sirupsen/arcticcreatures.m
this will output
func
andfile
not method.