Non duplicate intializers

In this release the descriptor's .initializers array must not contain duplicate initializers.

function init() {}

const Stamp = compose({ initializers: [init] }).compose({ initializers: [init] });
const stampInitializers = Stamp.compose.initializers;

In previous release the array would contain 2 items:
stampInitializers.length === 2

In this release the array will contain only unique item, i.e. one:
stampInitializers.length === 1