JSON decode failed on FreeBSD
When i compile master branch on FreeBSD 11.2 and FreeBSD 12 using both gcc and clang i get this error:
```
[2019-06-07 03:56:16] [xx.xx.x.xxx] JSON decode failed: "Invalid escape character in string."
[2019-06-07 03:56:26] [yyy.yy.yyy.yyy] JSON decode failed: "Invalid escape character in string."

```
When i compile it on Ubuntu and use xmrig-proxy on same miners no errors accured.