Crash on old nodejs: 'async' dependency version not fixed

[Chnapy]

Hi,

I have a project using nodejs 4 which use fluent-ffmpeg ^2.0.1.
It worked like a charm until that a README fix broke my Travis.

It crash on the require('fluent-ffmpeg').

Stacktrace:

/.../node_modules/async/dist/async.js:52
    function apply(fn, ...args) {
                       ^^^

SyntaxError: Unexpected token ...
    at exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:387:25)
    at Object.Module._extensions..js (module.js:422:10)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Module.require (module.js:367:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/.../node_modules/fluent-ffmpeg/lib/processor.js:7:13)

It crash like this with nodejs 4 and 5. But it works with nodejs 8, 9, and 11. I didn't test with other versions.
After a little investigation I saw that the async dependency version in the package.json is definitely in freewheel !

node-fluent-ffmpeg/package.json

Line 27 in d74149d

"async": ">=0.2.9",

Actually, when I look to my async version in my node_modules, it's 3.1.0 !

It's not safe to let a dependency change major version. I now have an app which worked before and not anymore without changing anything in its code.