Memory leak in mjson library

[Macok]

There is a memory leak just discovered in mjson library, which this project is using.
bolerio/mjson#27

Here's some analysis of a heap dump, dumped from our application using your KubePing implementation.

I would suggest switching to more mature json parser, at least until mjson issue gets fixed.

[slaskawi]

Thanks @Macok for noticing. I proposed fix here: bolerio/mjson#28

[slaskawi]

Fixed by #38