Wrong links in docs for `mwc` branch

[DannyMoerkerke]

When I click on one of the links for a component in the Components table on this page https://github.com/material-components/material-web/tree/mwc it still links to the master branch, resulting in a 404.

For example, clicking on <mwc-button> links to https://github.com/material-components/material-web/tree/master/packages/button while this should be https://github.com/material-components/material-web/tree/mwc/packages/button.

[thecalamiity]

@EstebanG23 Might want to close this one as well

[treeder]

This is fixed looks like.