Added django 2.2 to supported versions and prepared for a 1.0.4 release

[marksweb]

This fixes #294 by adding django 2.2 back to the supported versions.

I've also included a new version number and changelog entry for 1.0.4 so that this is releasable.

[marksweb]

@jrief This corrects an issue in my release of 1.0.3 yesterday and bumps the version to 1.0.4 so shouldn't require any extra changes before release.

So I'm hoping that this PR can be the first to go through the process of the automated release.

[marksweb]

@jrief The warning coming from the pypi action suggests that the token for test.pypi.org needs checking, but for security you can't view secret values on here.

It looks like you are trying to use an API token to authenticate in the package index and your token value does not start with "pypi-" as it typically should.

I also bumped the version number and did the changelog in this PR, but noticed you'd also bumped the version in master ready for this change.

[marksweb]

@jrief After adding these actions to some more repos, like django-sekizai and django-classy-tags, I think the pull_request trigger works differently than I expected. Therefore I've moved the test pypi action to trigger on pushes to master. So it'll trigger once a PR is merged and provide some reassurance that the package will build.