Fixes inconsistent encoding behavior.

[emmnx]

Python encodes ASCII by default and escapes the unicode characters.
This fix enforces utf-8.

Python 3.5.2 (default, Nov 23 2017, 16:37:01) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ipfsapi
>>> api = ipfsapi.connect('127.0.0.1', 5001)
>>> val = {"key": "Value, não é?"}
>>> api.add_json(val)
'QmNRzhk1e4cHYpqej7LjguBd5fP4uLyVYTQFfJFGm9ESLQ'
>>> api.get_json('QmNRzhk1e4cHYpqej7LjguBd5fP4uLyVYTQFfJFGm9ESLQ')
{'key': 'Value, não é?'}
>>> 

This is ok, expected behavior.

https://ipfs.io/ipfs/QmNRzhk1e4cHYpqej7LjguBd5fP4uLyVYTQFfJFGm9ESLQ <-- Ok here as well.

[ntninja]

Thanks for finding this! This really shouldn't be happening. 🙂

[ntninja]

Was merged as part of #168 for py-ipfs-http-client.