Upgrade to Babel 6

modules.js

"devDependencies": {
  "babel-plugin-syntax-class-properties": "^6.0.14",
  "babel-preset-react": "^6.1.2",
  "eslint": "^1.9.0",
  "eslint-loader": "^1.1.1",
  "babel-core": "^6.1.2",
  "babel-loader": "^6.0.1",
  "babel-preset-es2015": "^6.1.2",
},

webpack.config.js

module.exports = {
  entry: {
    overview: './resources/assets/js/overview.jsx'
  },
  output: {
    path: __dirname + "/public/assets/js",
    filename: "[name].js"
  },
  module: {
    loaders: [
      {
        test: /\.jsx|.js$/,
        exclude: /node_modules/,
        loader: 'babel-loader',
        query: {
          plugins: ["syntax-class-properties"],
          presets: ["es2015", "react"]
        }
      },
      {
        test: /\.jsx|.js$/,
        exclude: /node_modules/,
        loader: 'eslint-loader'
      },
      {
        test: /\.json$/,
        exclude: /node_modules/,
        loader: 'json-loader'
      }
    ]
  },
  resolve: {
    extensions: ['', '.js', '.jsx']
  }
}