fauna uploads fail in python 3 unicode error

[lmoncla]

When uploading new fasta files to fauna with python 3, upload.py fails at lines 59, 102, and 148 with: AttributeError: 'str' object has no attribute 'decode'. This does not occur with python 2.

[rneher]

none of nextstrain python is currently python3 conform. We should address that soon though. unicode is the default string in python3 and the decode behavior has changed.