Rename ExperimentalSpreadProperty

[duailibe]

What version of TypeScript are you using?

2.6.2

What version of typescript-eslint-parser are you using?

master

What code were you trying to parse?

const foo = { ...bar };

What did you expect to happen?

An SpreadElement or SpreadProperty should be in the AST, not ExperimentalSpreadProperty, since they are not considered experimental anymore (microsoft/TypeScript@39b9163)?

I'm not exactly sure how this should go but would make things a lot easier to maintain in prettier (for example prettier/prettier#3681) :-)

I can help with this, just need a direction (cc @JamesHenry)

[JamesHenry]

Thanks @duailibe! As now discussed on the PR, currently ESLint's policy dictates that because this is only stage 3, it is still experimental.