SourceMap directory is incorrect

[grantralls]

By the tsc config, ts expects the source maps to be in sketch/sketch/build.js.map. The source maps are actually generated into build/build.js.map. I was able to fix the issue in my own project by changing the map root setting in tsconfig to ../build.

You can confirm the issue by walking through the following process...

1. clone a clean copy of the repo.
2. npm i
3. npm run start-compile
4. check the last line in build/build.js

[grantralls]

It should be noted that the sourceRoot also needs to be updated to get the proper sources. I decided to remove both options sourceRoot and mapRoot to see if the automatic TS settings would do the trick and it did!

[Gaweph]

Good catch. Sorry for delay in responding. If you would like to do a PR with the relevant changes I would be happy to approve 👍

[grantralls]

#27