fix: swap mpid origin

[mtempranoWalla]

Summary

When in the mParticle back office the connection with optimizely is using the mparticle ID rather than the default one, the tracking event is trying to get the mpid from the userIdentities object but I can’t see it present in said object when debugging, nor any reference of getting mpid from it in the documentation. I see that this id is already present in the window object by that point, so I have changed it to mParticle.Identity.getCurrentUser().getMPID() instead.

This issue is only reproducible when:

• In the mParticle back office the id used for identifying events is changed from the default one to the mparticle ID.
• The client implementation sets a specific optimizely sdk version in the window object.
• The FullStack sdk is used

This issue causes:

• Events to not be tracked properly (experiment conversions don't happen) since it's using the default id instead of the specified one.

I'm aware that there might be an alternative that I haven't considered, therefore feel free to modify, change or discard this PR if it doesn't fit your needs. Thanks for the help anyways.

[rmi22186]

@mtempranoWalla - Thanks for the PR! Our team will review this shortly and let you know if we have any questions.

[atomasaltes]

LGTM!

[rmi22186]

@mtempranoWalla - This has been merged and released. If you use NPM it is version 2.1.6. Otherwise if you load us via snippet/cdn, you will get this automatically as cache busts (~10 min - 1 hr depending on browser settings).