TST: Fix error in assert_produces_warning.

When I copied this over and sent to @cpcloud,
I thought the indentation was wrong and changed it.
Turned out I was wrong -- sorry about that!

Now all the doctests pass...

Author: jtratner

pandas/util/testing.py

@@ -790,5 +790,5 @@ def assert_produces_warning(expected_warning=Warning, filter_level="always"):
         if expected_warning:
             assert saw_warning, ("Did not see expected warning of class %r."
                                  % expected_warning.__name__)
-            assert not extra_warnings, ("Caused unexpected warning(s): %r."
-                                        % extra_warnings)
+        assert not extra_warnings, ("Caused unexpected warning(s): %r."
+                                    % extra_warnings)