Support .finally(...)

[KamasamaK]

Promise.prototype.finally is introduced in ES2018, but the README indicates that it is "not available".

[ainthek]

+1

[tmgldn]

This nearly stopped me from using this library 😬

Thanks @KamasamaK for confirming

[tmgldn]

added a pr:
#46

[analog-nico]

I just merged @tbjgolden ’s PR #46 which clarifies this. With node v10 and above you can write these:

rp(...)
    .then(...)
    .catch(...)
    .finally(...)

rp(...)
    .catch(...)
    .finally(...)

rp(...)
    .then(...)
    .finally(...)

But not:

rp(...)
    .finally(...)

Until the direct finally call is supported, you can use:

rp(...).promise()
    .finally(...)

I leave this issue open until that last case without using .promise() is supported as well.