Unknown word (5:1)

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