Change unicode() to str()
Change unicode() to str()

Python 3 dropped support for unicode() and renamed it to str()
This commit accomodates that change.

Read more at -
https://docs.python.org/dev/howto/pyporting.html#text-versus-binary-data

Fix #460

datawire/ambassador,datawire/ambassador,datawire/ambassador,datawire/ambassador,datawire/ambassador