AddressBookGuiTest#cleanup(): Change throws declaration to Exception
AddressBookGuiTest#cleanup(): Change throws declaration to Exception

AddressBookGuiTest#cleanup() throws a specific exception,
TimeoutException.

We can use a more generic exception just like the rest of the test
methods in the code base.

Let's change the throws declaration from TimeoutException to Exception.

CS2103R-Eugene-Peh/addressbook-level4,damithc/addressbook-level4,se-edu/addressbook-level3,damithc/addressbook-level4,CS2103R-Eugene-Peh/addressbook-level4,CS2103R-Eugene-Peh/addressbook-level4,damithc/addressbook-level4