Build failures under Go 1.18 due to js.Wrapper removal

[ralimi]

js.Wrapper was removed in Go 1.18. Thus, this library fails to build under Go 1.18 due to e.g., https://github.com/norunners/vert/blob/main/value.go#L30.

See golang/go#50310 for some additional background; the proposal to reinstate it was declined.

[nitram509]

Fix available in #19

[norunners]

Thank you for the contribution, I reviewed the pull request.