Related to  #11474 and #12815.

The following should be added to `package.json` of `pdfjs-dist` for `worker-loader`.
```
  "peerDependenciesMeta": {
    "worker-loader": {
      "optional": true
    }
  }
```

npm v7 installs `peerDependencies` by default. We can see that calling `npm install pdfjs-dist` in an empty directory will install `webpack` and others in `node_modules`.

> In npm versions 3 through 6, peerDependencies were not automatically installed, and would raise a warning if an invalid version of the peer dependency was found in the tree. As of npm v7, peerDependencies are installed by default.

- https://docs.npmjs.com/cli/v7/configuring-npm/package-json#peerdependencies
- https://github.blog/2020-10-13-presenting-v7-0-0-of-the-npm-cli/

We can make `worker-loader` optional with `peerDependenciesMeta`.

- https://docs.npmjs.com/cli/v7/configuring-npm/package-json#peerdependenciesmeta
- https://github.com/npm/rfcs/issues/221
}
    const { stableVersion, betaVersion } = config;
    replaceInFile(
      GH_PAGES_DIR + "/getting_started/index.html",
      /STABLE_VERSION/g,
      stableVersion
    );
    replaceInFile(
      GH_PAGES_DIR + "/getting_started/index.html",
      /BETA_VERSION/g,
      betaVersion
    );
    
    const groupClass = betaVersion ? "btn-group-vertical centered" : "";
    const hiddenClass = betaVersion ? "" : "hidden";
    replaceInFile(
      GH_PAGES_DIR + "/getting_started/index.html",
      /GROUP_CLASS/g,
      groupClass
    );
    replaceInFile(
      GH_PAGES_DIR + "/getting_started/index.html",
      /HIDDEN_CLASS/g,
      hiddenClass
    );
    console.log("Done building with wintersmith.");
    done();
  });
});
function ghPagesGit(done) {