fix: loading plugin returns chain of promises effect

[JWF-Spiria]

Return the chain promise to propagate the throw error and continue the chaining normally.
Fix the Unhandled Promise Rejection

Closes #906

[semoal]

Looks great to me and has a lot of sense, could you add a test for this?
I have a plan to introduce a big feature inside loading plugin and I don't want to break any suit case

[JWF-Spiria]

Well I don't know if it would add anything. You already have tests that cover the propagation of the effect error. The new code simply prevent the warning.

[JWF-Spiria]

I guess we could put this in the describe function?

process.on('unhandledRejection', (err) => { fail(err); });

[semoal]

Thanks for the contribution mate, I'll release this with 2.1.0 in aprox 1 week more or less it will be released. :)