JSON_NO_EXTRA_WHITESPACE error

https://github.com/esnme/ultrajson/blob/master/lib/ultrajsonenc.c#L799
```c
#ifndef JSON_NO_EXTRA_WHITESPACE
          Buffer_AppendCharUnchecked (buffer, ' ');
#endif
```
it should be 
```c
#ifndef JSON_NO_EXTRA_WHITESPACE
          Buffer_AppendCharUnchecked (enc, ' ');
#endif
```