Type of Object.groupBy and its callback wrong

[zbynek]

https://github.com/google/closure-compiler/blob/f2cc20715e86c7dafd6de0f9e06eb2da693903f3/externs/es6.js#L2456

produces multiple signatures that are incorrect. Looks like it was interpreted as

[ function(T, number=): string ] |symbol|number

rather than

function(T, number=): [ string|symbol|number ]

[jDramaix]

Fixed in google/closure-compiler@7a92f58

I'll create a 1.4.0-RC2 once this change is available in a new in closure-compiler version

[zbynek]

@jDramaix do you also want to include #186 in RC2?

[jDramaix]

@jDramaix do you also want to include #186 in RC2?

I just merged the fix so it will be included