Correct type.invalid.super.wildcard message

[zcai1]

The arguments passed to type.invalid.super.wildcard were not in the right order, so this PR fixes it.

The behavior of this check should be valid as described in: typetools#5006

We encountered a warning in:

import java.util.Set;
import org.checkerframework.checker.nullness.qual.*;

public class TestSet {
    void foo(Set<Object> s1, Set<? super Object> s2) {
        s1.retainAll(s2);
    }
}

because the capture of Set<? super Object> is Set<Object> and its implicit upper bound is @Nullable.

[wmdietl]

Thanks!