Log Caller does not work with json logging

[kris-runzer]

I've noticed that using NewJSONLogger that caller is always an emtpy {} when logging:
​
logger = log.NewJSONLogger(os.Stderr)
logger = log.NewContext(logger).With("caller", log.DefaultCaller)
​logger.Log()
​
Results in the following log output:
​
{"caller":{}}

[ChrisHines]

Thanks for the issue report.

[ChrisHines]

I have added a test case for this issue: c158bb5.

The fix is implemented in the upstream package gopkg.in/stack.v1: go-stack/stack@03cd31e.

To get the fix, run:

go get -u gopkg.in/stack.v1
go get -u github.com/go-kit/kit