function buildBabelOptions(script) {
  return {
    presets: script.presets || ["react", "es2015"],
    plugins: script.plugins || ["proposal-class-properties", "proposal-object-rest-spread", "transform-flow-strip-types"],
    sourceMaps: "inline"
  };
}
Builds the Babel options for transforming the specified script, using some
sensible default presets and plugins if none were explicitly provided.