Stick to lowercase lib enums in tsconfig.json files

[peterblazejewicz]

just FYI:
That's completely minorish issue, non-relevant to the excellent content. The schema for tsconfig.json does not allow uppercase versions string enums for 'lib', so some editors (VSCode) mark the project(s) as containing error - if they validate tsconfigs content.
http://json.schemastore.org/tsconfig

Thanks!