Top level fields with skip/include directives ignored for mutations

[rramaa-dh]

This is duplicate of #65.
After the fix for that issue, now the top level fields are skipped/included for queries. But the same does not work for mutations

query getTodos @skip(if: true) {
    // this works and the query is skipped
}

mutation createTodos @skip(if: true) {
    // this does not work and the mutation is executed
}