* handle disordered rest parameter in function expressions
* remove spaces [lint]
* polish function parameters validation
* add test with arrow function and comma after rest parameter [babel-parser]
These are now enabled by default:
- objectRestSpread (2018)
- asyncGenerators (2018)
- optionalCatchBInding (2019)
- jsonStrings (2019)
TODO (after this commit):
- [ ] Deprecate the `@babel/plugin-syntax-*` packages.
- [ ] Deprecate the `@babel/plugin-proposal-*` packages.
- [ ] Create the `@babel/plugin-transform-*` packages.
