Set devtool conf with 'source-map'

[nicolaspayot]

Here's a proposal to change devtool conf from cheap-eval-source-map with source-map:

Source file doesn't seem to be found with cheap-eval-source-map as shown on the screenshot:

whereas it's correctly working with source-map:

[Swiip]

I change this conf myself in every project I generate... It's slower but needed.

[getglad]

I would suggest cheap-source-map - if I am reading the docs correctly, it should run faster.

https://webpack.github.io/docs/configuration.html#devtool

[Swiip]

Faster yes, but there is a trade off between speed and quality. Previous configuration was the fastest but was really bad