feat(gatsby): use cheap-module-source-map devtool webpack config in develop mode for easier debugging (#10083)
feat(gatsby): use cheap-module-source-map devtool webpack config in develop mode for easier debugging (#10083)

Closes #6278

Sourcemaps are not currently working on gatsby v2. This fixes that on 1 string.
gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,0x80/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,0x80/gatsby,ChristopherBiscardi/gatsby,0x80/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby