add back automation to push built plugin to dist repo

[tharsheblows]

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Bug Report

In 4.0.0, the Travis CI workflow which ported the built plugin to the distribution repo broke. It was removed in 4.0.1. The distribution repo is tied to the Stream package in Packagist and needs to be kept up to date with releases.

nb: this could be a tooling only update and if it is released on its own, may not need pushing to the WordPress plugins repo, although this should be discussed.

Expected Behavior

Releases should appear on Packagist via the distribution repo.

Actual Behavior

Releases are not pushed to the distribution repo.

Steps to Reproduce the Problem

1. Look at the 4.0.1 release in this repo
2. Notice that it does not appear in the distribution repo or on Packagist.