doc: change godoc to go.dev (#45)

Co-authored-by: Abhinav Gupta <mail@abhinavg.net>

README.md

@@ -15,8 +15,8 @@ Stable: No breaking changes will be made before 2.0.
 Released under the [MIT License].
 
 [MIT License]: LICENSE.txt
-[doc-img]: https://godoc.org/go.uber.org/multierr?status.svg
-[doc]: https://godoc.org/go.uber.org/multierr
+[doc-img]: https://pkg.go.dev/badge/go.uber.org/multierr
+[doc]: https://pkg.go.dev/go.uber.org/multierr
 [ci-img]: https://travis-ci.com/uber-go/multierr.svg?branch=master
 [cov-img]: https://codecov.io/gh/uber-go/multierr/branch/master/graph/badge.svg
 [ci]: https://travis-ci.com/uber-go/multierr