Default tsc --init to es2016

[orta]

ES5 is a pretty low target, I doubt most folks making a new TypeScript project want something that old.

So, I propose we think of the default target in --init as being "5 years" ago, and generally try to keep that in sync. E.g. sometime next year we'd accept a PR which sets it to be es2017.

[AviVahl]

Worth noting that "dom" lib was included by default when target was set to "es5" (because "lib" is commented out in tsc --init template). May no longer be the case with this change.

[DanielRosenwasser]

I would hope that dom isn't excluded as a result of target - that would be a confusing upgrade step. 😬

[orta]

This got OK'd at a design meeting 👍🏻