Fix bug where fields is ignored if exceed_limit is True

[marceloandrioni]

This fixes #55.

Before the fix the fields was ignored when exceed_limit was True, e.g.:

import restapi

rest_url = 'https://sampleserver6.arcgisonline.com/arcgis/rest/services'
ags = restapi.ArcServer(rest_url)
usa = ags.getService('USA') #/USA/MapServer -> restapi.common_types.MapService
cities = usa.layer('Cities') # or can use layer id: usa.layer(0)

where = "st = 'CA' and pop2000 > 100000"

featureSet = cities.query(where=where, fields=["areaname", "capital"],
                          exceed_limit=True)
print(featureSet[0]["properties"])
# {
#   "areaname": "Anaheim",
#   "capital": "N",
#   "class": "city",
#   "objectid": 169,
#   "pop2000": 328014,
#   "st": "CA"
# }

after the fix:

featureSet = cities.query(where=where, fields=["areaname", "capital"],
                          exceed_limit=True)
print(featureSet[0]["properties"])
# {
#   "areaname": "Anaheim",
#   "capital": "N"
# }

[philnagel]

Thank you for the PR!