Simple PEP8 issues.

lms/djangoapps/courseware/models.py

@@ -108,7 +108,6 @@ class StudentModuleCache(object):
         else:
             self.cache = []
 
-
     @classmethod
     def cache_for_descriptor_descendents(cls, course_id, user, descriptor, depth=None,
                                          descriptor_filter=lambda descriptor: True,
@@ -138,7 +137,6 @@ class StudentModuleCache(object):
 
             return descriptors
 
-
         descriptors = get_child_descriptors(descriptor, depth, descriptor_filter)
 
         return StudentModuleCache(course_id, user, descriptors, select_for_update)