Existential return type annot in arrow function confused with *= operator #6666
Description
Issue originally reported by @mroch in babel/babylon#772
Input Code
const x = ():*=>{}Babylon/Babel Configuration
flow plugin enabled
Expected Behavior
Should be an arrow function with a * type annotation
Current Behavior
"Unexpected token" pointing at the *=
Your Environment
babylon7-7.0.0-beta.12 and babylon6-6.17.1: http://astexplorer.net/#/gist/a4d0ae75b6e1db95a394fd591f31a8c9/8cb4469554642dd1ce1bae05742af3146406d8af
Flow parses it correctly