Unknown word (5:1) na importação do bootstrap

Estou recebendo o seguinte erro quando tento importar o bootstrap:

Failed to compile.

./node_modules/css-loader!./node_modules/style-loader!./node_modules/css-loader!./node_modules/bootstrap/dist/css/bootstrap.css
Module build failed: Unknown word (5:1)

  3 | // load the styles
  4 | var content = require("!!../../../css-loader/index.js!./bootstrap.css");
> 5 | if(typeof content === 'string') content = [[module.id, content, '']];
    | ^
  6 | // add the styles to the DOM
  7 | var update = require("!../../../style-loader/addStyles.js")(content, {});
  8 | if(content.locals) module.exports = content.locals;

 @ ./node_modules/bootstrap/dist/css/bootstrap.css 4:14-131 13:3-17:5 14:22-139
 @ ./src/main.js
 @ multi (webpack)-dev-server/client?http://localhost:8081 webpack/hot/dev-server ./src/main.js

Meu webpack.config.json

var path = require('path')
var webpack = require('webpack')

module.exports = {
  entry: './src/main.js',
  output: {
    path: path.resolve(__dirname, './dist'),
    publicPath: '/dist/',
    filename: 'build.js'
  },
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          'vue-style-loader',
          'css-loader'
        ],
      }, {
        test: /\.vue$/,
        loader: 'vue-loader',
        options: {
          loaders: {
          }
          // other vue-loader options go here
        }
      },
      {
        test: /\.js$/,
        loader: 'babel-loader',
        exclude: /node_modules/
      },
      {
        test: /\.(png|jpg|gif|svg)$/,
        loader: 'file-loader',
        options: {
          name: '[name].[ext]?[hash]'
        }
      },
      {
        test: /\.css$/,
        loader: 'style-loader!css-loader'
      },
      { test: /\.(woff|woff2)(\?v=\d+\.\d+\.\d+)?$/, loader: 'url-loader?limit=10000&mimetype=application/font-woff' },
      { test: /\.ttf(\?v=\d+\.\d+\.\d+)?$/, loader: 'url-loader?limit=10000&mimetype=application/octet-stream' },
      { test: /\.eot(\?v=\d+\.\d+\.\d+)?$/, loader: 'file-loader' },
      { test: /\.svg(\?v=\d+\.\d+\.\d+)?$/, loader: 'url-loader?limit=10000&mimetype=image/svg+xml' }
    ]
  },
  resolve: {
    alias: {
      'vue$': 'vue/dist/vue.esm.js'
    },
    extensions: ['*', '.js', '.vue', '.json']
  },
  devServer: {
    historyApiFallback: true,
    noInfo: true,
    overlay: true
  },
  performance: {
    hints: false
  },
  devtool: '#eval-source-map'
}

if (process.env.NODE_ENV === 'production') {
  module.exports.devtool = '#source-map'
  // http://vue-loader.vuejs.org/en/workflow/production.html
  module.exports.plugins = (module.exports.plugins || []).concat([
    new webpack.DefinePlugin({
      'process.env': {
        NODE_ENV: '"production"'
      }
    }),
    new webpack.optimize.UglifyJsPlugin({
      sourceMap: true,
      compress: {
        warnings: false
      }
    }),
    new webpack.LoaderOptionsPlugin({
      minimize: true
    })
  ])
}