Support effective_status in campaigns response (#293)

Author: juanshishido

twitter_ads/campaign.py

@@ -227,6 +227,7 @@ class Campaign(Analytics, Resource, Persistence, Batch):
 resource_property(Campaign, 'created_at', readonly=True, transform=TRANSFORM.TIME)
 resource_property(Campaign, 'currency', readonly=True)
 resource_property(Campaign, 'deleted', readonly=True, transform=TRANSFORM.BOOL)
+resource_property(Campaign, 'effective_status', readonly=True)
 resource_property(Campaign, 'id', readonly=True)
 resource_property(Campaign, 'reasons_not_servable', readonly=True)
 resource_property(Campaign, 'servable', readonly=True, transform=TRANSFORM.BOOL)