From the babel 6 Release notes:
Since Babel is focusing on being a platform for JavaScript tooling and not an ES2015 transpiler, we’ve decided to make all of the plugins opt-in. This means when you install Babel it will no longer transpile your ES2015 code by default.
In my setup I installed the es2015 preset
npm install --save-dev babel-preset-es2015
or with yarn
yarn add babel-preset-es2015 --dev
and enabled the preset in my .babelrc
{
"presets": ["es2015"]
}