added asset testcases

Author: ishaileshmishra

contentstack/__init__.py

@@ -11,7 +11,6 @@
 from .asset import Asset
 from .asset_library import AssetLibrary
 from .config import Config
-from .query_result import QueryResult
 from .content_type import ContentType
 from .errors import HTTPError, ConfigError
 from .group import Group

contentstack/asset_library.py

@@ -34,7 +34,7 @@
 """
 
 
-class AssetLibrary():
+class AssetLibrary:
 
     def __init__(self):
         self.count = 0