Use native Object.assign instead of xtend

[Jimmy Wärting]

xtend can easily be replaced with Object.assign

This reduce the dependencies and possible also avoid duplicated versions where some package don't use the same version range for the xtend package

// immutable
Object.assign({}, a, b)

// mutable
Object.assign(a, b)

[Vincent Weevers]

SGTM. Would you be up for making a PR?

[Jimmy Wärting]

sure