docs(guides): change CleanWebpackPlugin arguments usage

[Ivocin]

CleanWebpackPlugin released v2.0.0 and the API has a breaking change: No configuration is needed for standard usage (cleans webpack's output.path).

new CleanWebpackPlugin(['dist/*']) with the new version clean-webpack-plugin installed above will cause an error:
"Error: clean-webpack-plugin only accepts an options object. See: https://github.com/johnagan/clean-webpack-plugin#options-and-defaults-optional "

[EugeneHlushko]

It was released a day ago, suggesting to add a comment like this or think in this direction

[EugeneHlushko]

It looks good to me, i am hesitant if we should also add a + to the comment line so its highlighted....

[Ivocin]

It looks good to me, i am hesitant if we should also add a + to the comment line so its highlighted....

add a + is a good idea, because the previous demo code above doesn't have this line.

[montogeek]

Thanks!