Treq now requires bytes, not str, so encoding is up to the client

[aren]

See twisted/treq#151.

[jessewgibbs]

@aren thanks for the contribution.

@rokob can you review?

[rokob]

My main concern is that this needs to work with both Python 2 and 3. I think we have tests for both and it looks like it is passing so it probably is okay. Let me just double check, but otherwise it looks good to me.

[aren]

I did test on both 2 and 3, but another set of eyes is always appreciated.

[AdrianLC]

👍 I just tested this on python 3.6 seems to work. Really lucky I found the fix that you just sent today, thanks!

[rokob]

So I played around with this, encode can raise UnicodeDecodeError and UnicodeEncodeError depending on the value of the receiver, so I changed this to handle those exceptions, otherwise looks good to me.