Converted DEFAULT_RETENTION_DAYS env var to an integer

lambda_ebs_snapshots.py

@@ -10,7 +10,7 @@ deletion after a number of retention days.
 """
 
 MIN_RETENTION_COUNT = int(os.environ['MIN_RETENTION_COUNT'])
-RETENTION_DAYS_DEFAULT = os.environ['DEFAULT_RETENTION_DAYS']
+RETENTION_DAYS_DEFAULT = int(os.environ['DEFAULT_RETENTION_DAYS'])
 SNAPSHOT_TAG = os.environ['SNAPSHOT_TAG']
 RETENTION_TAG = os.environ['RETENTION_TAG']
 DELETE_TAG = os.environ['DELETE_TAG']