Grunt example does not work

[DmitryGonchar]

Says:

Warning: Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.
 - configuration.entry should be one of these:
   object { <key>: non-empty string | [non-empty string] } | non-empty string | [non-empty string] | function
   The entry point(s) of the compilation.
   Details:
    * configuration.entry should be an object.
    * configuration.entry should be a string.
    * configuration.entry[1] should be a string.
    * configuration.entry should be an instance of function
      function returning an entry object or a promise.. Use --force to continue.

webpack config has entry: property, works via npm scripts
Using Webpack 3