Manual: slicing syntax in example doesn't match documentation

Example in https://gitlab.redox-os.org/redox-os/ion/blob/master/manual/src/control/02-loops.md#chunked-iterations has

{1..=10}

but the ..= syntax isn't documented in https://gitlab.redox-os.org/redox-os/ion/blob/master/manual/src/slicing.md#ranges-slicing-syntax.