Fixup GH Pages deploy instructions

These work regardless of whether you already have a gh-pages branch.

Author: gaearon

scripts/build.js

@@ -32,11 +32,12 @@ webpack(config).run(function(err, stats) {
  console.log('You can now deploy it to ' + homepagePath + '.');
  console.log('For example, if you use GitHub Pages:');
  console.log();
+ console.log(' git commit -am "Save local changes"');
  console.log(' git checkout -B gh-pages');
  console.log(' git add -f build');
  console.log(' git commit -am "Rebuild website"');
- console.log(' git push origin :gh-pages');
- console.log(' git subtree push --prefix build origin gh-pages');
+ console.log(' git filter-branch -f --prune-empty --subdirectory-filter build');
+ console.log(' git push -f origin gh-pages');
  console.log(' git checkout -');
  console.log();
  } else {