Change default arguent value for clarity

It is valie to pass None in service_params arguments, so make it the default.

server/lib/python/cartodb_services/cartodb_services/here/geocoder.py

@@ -52,7 +52,7 @@ class HereMapsGeocoder(Traceable):
         'strictlanguagemode'
         ] + ADDRESS_PARAMS
 
-    def __init__(self, app_id, app_code, logger, service_params={}, maxresults=DEFAULT_MAXRESULTS):
+    def __init__(self, app_id, app_code, logger, service_params=None, maxresults=DEFAULT_MAXRESULTS):
         service_params = service_params or {}
         self.app_id = app_id
         self.app_code = app_code

server/lib/python/cartodb_services/cartodb_services/here/routing.py

@@ -30,7 +30,7 @@ class HereMapsRoutingIsoline(Traceable):
         'quality'
     ]
 
-    def __init__(self, app_id, app_code, logger, service_params={}):
+    def __init__(self, app_id, app_code, logger, service_params=None):
         service_params = service_params or {}
         self._app_id = app_id
         self._app_code = app_code

server/lib/python/cartodb_services/cartodb_services/mapzen/geocoder.py

@@ -17,7 +17,7 @@ class MapzenGeocoder(Traceable):
     CONNECT_TIMEOUT = 10
     MAX_RETRIES = 1
 
-    def __init__(self, app_key, logger, service_params={}):
+    def __init__(self, app_key, logger, service_params=None):
         service_params = service_params or {}
         self._app_key = app_key
         self._url = service_params.get('base_url', self.BASE_URL)

server/lib/python/cartodb_services/cartodb_services/mapzen/isochrones.py

@@ -20,7 +20,7 @@ class MapzenIsochrones:
         "car": "auto"
     }
 
-    def __init__(self, app_key, logger, service_params={}):
+    def __init__(self, app_key, logger, service_params=None):
         service_params = service_params or {}
         self._app_key = app_key
         self._logger = logger

server/lib/python/cartodb_services/cartodb_services/mapzen/matrix_client.py

@@ -23,7 +23,7 @@ class MatrixClient(Traceable):
     READ_TIMEOUT = 60
     CONNECT_TIMEOUT = 10
 
-    def __init__(self, matrix_key, logger, service_params={}):
+    def __init__(self, matrix_key, logger, service_params=None):
         service_params = service_params or {}
         self._matrix_key = matrix_key
         self._logger = logger

server/lib/python/cartodb_services/cartodb_services/mapzen/routing.py

@@ -33,7 +33,7 @@ class MapzenRouting(Traceable):
     METRICS_UNITS = 'kilometers'
     IMPERIAL_UNITS = 'miles'
 
-    def __init__(self, app_key, logger, service_params={}):
+    def __init__(self, app_key, logger, service_params=None):
         service_params = service_params or {}
         self._app_key = app_key
         self._logger = logger