[in_app_purchase] Fix CHANGELOG for 0.2.0.

[mvanbeusekom]

PR #4458 was merged without having the version updated and the functionality is now published as part of in_app_purchase_ios version 0.2.0 (that was release with PR #4094).

This PR adds a belated correction to version 0.2.0 in the CHANGELOG to ensure the changes made in #4458 don't go undocumented.

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/plugins repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
  • Only a documentation change in the CHANGELOG.md and a corresponding version bump in pubspec.yaml. So no new tests were added.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[stuartmorgan-g]

[ ] I added new tests to check the change I am making, or this PR is test-exempt.

• Only a documentation change in the CHANGELOG.md and a corresponding version bump in pubspec.yaml. So no new tests were added.

It's not obvious from the link, but this is actually test-exempt (as evidenced by the bot not commenting); pubspec.yaml is considered okay by the bot, even though it's not listed on the wiki (I'll ask Hixie about that, actually). So you can check the box.

[stuartmorgan-g]

LGTM with nits

[stuartmorgan-g]

Why the change from . to ;? This was right before.

[mvanbeusekom]

since it is no longer the last element in the list. In Dutch you add a semi-colon for each item in the list except for the last item which ends with a period to indicate the end of the list. I always thought this is the same in English.

[stuartmorgan-g]

We've never treated the changelog as a single-sentence list grammatically, but as a series of independent sentences. Otherwise the capitalization would be wrong, and multi-sentence entries (like this one, in fact) would be very strange.