Remove dependency on Apache's Commons-Lang

[mannodermaus]

This library includes all of commons-lang because of one single usage in capitalizing String input. Since the library footprint of commons-lang, with its roundabout 3000 methods, is comparatively big in relation to its usefulness in Postman, I am proposing to get rid of the dependency and roll our own implementation of StringUtils.capitalize().

[ndtaylor]

Sounds reasonable.