docs: add @landluck and @wjw-gavin to core team

[chenjiahan]

Thanks @landluck and @wjw-gavin for your contribution to Vant and Vant Weapp, you deserve to be added to the core team list.

Let's build Vant / Vant Weapp better together .^_^

[wjw-gavin]

Thanks to you and congratulations to myself!😂 This is my first participation in open source, there may be a lot of shortcomings, please you more guidance, I wish Vant and Vant Weapp better and better.🎉🎉