Deploying a second time does not remove previous build's files

[NathanJang]

When I run github-pages:commit, and there already exists previously-deployed files on the gh-pages branch, they are not removed. Is this a design choice? I expected this to wipe the files and rebuild completely. I've run this a few times and the duplicate files in https://github.com/NathanJang/nathanjang.github.io/tree/9c2d576f0c301fae02bb83fff8613a9690c4ea09/assets is what happens.

Maybe it we just to configure the cp command in more detail, maybe on this line?

ember-cli-github-pages/lib/commands/commit.js

Line 50 in dd4498c

return runCommand('cp -R dist/* .', execOptions);

Thanks!