Fix method delegation in _flushfile

Required when the faked stream is already faked and the original fake also uses method delegation.

Author: aivarannamaa

src/cs50/cs50.py

@@ -49,7 +49,7 @@ def __init__(self, f):
         self.f = f
 
     def __getattr__(self, name):
-        return object.__getattribute__(self.f, name)
+        return getattr(self.f, name)
 
     def write(self, x):
         self.f.write(x)