nearly 3 years ago, #202 (comment) mentioned typescript won't be supported

Since then typescript has gained momentum, community and support by many in the js community (https://2019.stateofjs.com/javascript-flavors/typescript/)
While typescript is made by mozilla's sworn enemy, as programmers we strive for best of breed tools. Typescript is arguably a tool that many teams choose to use due to its abilities.

Typescript's support is currently done unofficially through community effort on https://github.com/DefinitelyTyped/DefinitelyTyped but it will make it so much easier to use node-convict if there will be official support for it within the project.

Please reconsider having typescript support.