Implement `IPython.utils.io.Tee.isatty`

A lot of libraries would call `sys.stdout.isatty()`, but `IPython.utils.io.Tee` does not implement `isatty`.

Let's add the method to avoid errors.

IPython/utils/io.py

@@ -75,6 +75,8 b' class Tee(object):'
         if not self._closed:
             self.close()
 
+    def isatty(self):
+        return False
 
 def ask_yes_no(prompt, default=None, interrupt=None):
     """Asks a question and returns a boolean (y/n) answer.