Fix parsing of newline between 'async' and 'function'

[existentialism]

Q	A
Fixed Issues?	Fixes #8696
Patch: Bug Fix?	Y
Major: Breaking Change?	N
Minor: New Feature?	N
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/9126/

[nicolo-ribaudo]

This code should throw:

export default async functionX () {}

https://babeljs.io/repl/build/9112/#?babili=false&browsers=&build=&builtIns=usage&spec=false&loose=true&code_lz=KYDwDg9gTgLgBAE2AMwIYFcA29UGcCeAdgMZzLokwCWEhAGnABQCUcA3gL5A&debug=false&forceAllTransforms=true&shippedProposals=true&circleciRepo=&evaluate=true&fileSize=false&timeTravel=false&sourceType=module&lineWrap=false&presets=&prettier=false&targets=&version=7.0.0&envVersion=7.0.0

[existentialism]

@nicolo-ribaudo nice catch