adds json to moduleFileExtensions in docs
adds json to moduleFileExtensions in docs

Under Jest, Enzyme fails to load due to its dependency 'Cheerio', which
requires its package.json file without specifying the '.json' file
extension. This can be mitigated by adding '.json' to the
mduleFileExtension Jest config item in a projet's package.json.

seejee/enzyme,toddw/enzyme,airbnb/enzyme,toddw/enzyme,dustinsanders/enzyme,dustinsanders/enzyme,airbnb/enzyme,seejee/enzyme