fixes error in Python 3.6 related to joining bytes and strings

[bretthandrews]

I tried to plot query results

from marvin.tools.query import Query
myfilter = 'nsa.z < 0.1'
q = Query(searchfilter=myfilter, returnparams=['cube.ra', 'cube.dec'])
r = q.run()
r.plot('cube.ra', 'cube.dec', show_plot=False)

which threw this error:

TypeError                                 Traceback (most recent call last)
<ipython-input-1-c3b3ca85694f> in <module>()
      3 q = Query(searchfilter=myfilter)
      4 r = q.run()
----> 5 r.plot('nsa.z', 'nsa.z', show_plot=False)

~/projects/sdss/sas/mangawork/manga/marvin/python/marvin/tools/results.py in plot(self, x_name, y_name, **kwargs)
   1553         # computes a list of plateifus in each bin
   1554         if return_plateifus and with_hist:
-> 1555             plateifus = self.getListOf('plateifu', return_all=True)
   1556             hdata = output[2] if return_figure else output
   1557             if 'xhist' in hdata:

~/projects/sdss/sas/mangawork/manga/marvin/python/marvin/tools/results.py in getListOf(self, name, to_json, to_ndarray, return_all)
    975             params = {'searchfilter': self.searchfilter, 'format_type': 'list',
    976                       'return_all': True, 'params': self.returnparams}
--> 977             output = self._interaction(url, params, calltype='getList')
    978         else:
    979             # only deal with current page

~/projects/sdss/sas/mangawork/manga/marvin/python/marvin/tools/results.py in _interaction(self, url, params, calltype, create_set, **kwargs)
    911         # send the request
    912         try:
--> 913             ii = Interaction(route=url, params=params, stream=True)
    914         except MarvinError as e:
    915             raise MarvinError('API Query {0} call failed: {1}'.format(calltype, e))

~/projects/sdss/sas/mangawork/manga/marvin/python/marvin/extern/marvin_brain/python/brain/api/api.py in __init__(self, route, params, request_type, auth, timeout, headers, stream)
     49         # sends the request
     50         if self.url:
---> 51             self._sendRequest(request_type)
     52         else:
     53             raise BrainError('No route and/or url specified {0}'.format(self.url))

~/projects/sdss/sas/mangawork/manga/marvin/python/marvin/extern/marvin_brain/python/brain/api/api.py in _sendRequest(self, request_type)
    216         else:
    217             # Check the response if it's good
--> 218             self._checkResponse(self._response)
    219
    220     def getData(self, astype=None):

~/projects/sdss/sas/mangawork/manga/marvin/python/marvin/extern/marvin_brain/python/brain/api/api.py in _checkResponse(self, response)
    168
    169             self.status_code = response.status_code
--> 170             self.results = self._get_content(response)
    171             self.response_time = response.elapsed
    172             if not self.results:

~/projects/sdss/sas/mangawork/manga/marvin/python/marvin/extern/marvin_brain/python/brain/api/api.py in _get_content(self, response)
    121         content_type = response.headers['Content-Type']
    122         if 'json' in content_type:
--> 123             data = self._get_json_data(response)
    124         elif 'octet-stream' in content_type:
    125             data = self._get_binary_data(response)

~/projects/sdss/sas/mangawork/manga/marvin/python/marvin/extern/marvin_brain/python/brain/api/api.py in _get_json_data(self, response, chunksize)
     99
    100         if self.stream:
--> 101             resstring = ''.join([chunk for chunk in response.iter_content(chunk_size=chunksize)])
    102             json_data = json.loads(resstring.decode())
    103         else:

TypeError: sequence item 0: expected str instance, bytes found