Correct parentActivity example in Activity Element docs.

Bug:
https://code.google.com/p/android/issues/detail?id=74474

Change-Id: I09d07a69d6aa0087e60443ed819541e979012948
(cherry picked from commit 0b54c6c74a28d7c96ffef80baaa0ddb6b9881ff9)
1 file changed