TEST: Fix invalid ast transformer in test.

The ast transformer used in test_interactiveshell.TestAstTransformError
had an incorrect method signature, causing it to raise a TypeError when
called, rather than the expected ValueError.  This change makes the test
transformer actually throw the expected error.

IPython/core/tests/test_interactiveshell.py

@@ -681,7 +681,7 b' class TestAstTransform2(unittest.TestCase):'
 
 class ErrorTransformer(ast.NodeTransformer):
     """Throws an error when it sees a number."""
-    def visit_Num(self):
+    def visit_Num(self, node):
         raise ValueError("test")
 
 class TestAstTransformError(unittest.TestCase):