Readme might be wrong

[Vishwaas]

It specifies that, "Source maps are always enabled unless explicitly disabled by specifying debug: false.". When I used use-babelrc file from code coverage which uses browserify preprocessor(https://github.com/cypress-io/code-coverage/blob/master/use-babelrc.js) and printed defaultOptions then debug is undefined. I had to explicityly set debug to true to get sourcemaps to work or else source maps only showed up if console.log was added in the code.
options.browserifyOptions=true

Related issue:
cypress-io/code-coverage#471