Please update goamz (again)

[Martin Packman]

As of r1685 of juju-core, we require r40 on goamz. Please pull in that
revision to avoid the following test failure in provider/ec2:

local_test.go:364:
    ...
... obtained []instance.Address =
[]instance.Address{instance.Address{Value:"i-4.example.com",
Type:"hostname", NetworkName:"", NetworkScope:"public"}}
... expected []instance.Address =
[]instance.Address{instance.Address{Value:"i-4.testing.invalid",
Type:"hostname", NetworkName:"", NetworkScope:"public"},
instance.Address{Value:"i-4.internal.invalid", Type:"hostname",
NetworkName:"", NetworkScope:"local-cloud"}}

Thanks!

Martin