fix!: Bump engine requirements android >= 10, ios >= 6

[breautek]

Platforms affected

Android / iOS

Motivation and Context

There were concerns raised during 5.0.0 release: https://lists.apache.org/thread/dzmm273b76pngtor6386s71yzf6lzxck

I’ve read the blog post and it mentions “The JavaScript of the plugin has
been upgraded to use ES6 features, such as let and const.”.
But the plugin engines still support cordova-android 6+.
Should we bump the engines to require latest cordova-android? Those new ES6
features won’t work on those old cordova-android versions.

To address these concerns, this caveat is noted in the release blog (see apache/cordova-docs#1335). While this is technically a breaking change it can be thought of a patch onto 5.0.1 and be included in our next patch or feature release.

Description

Bump engine versions in both plugin.xml and package.json
cordova-android >= 10 for min SDK 22 (cordova-android 9 also had minSDK 22 but dependent on jfrog)
cordova-ios >= 6 for iOS 11 minimum deployment

iOS 11 has good support for ES6 (however with some buggy behaviour)
SDK 22 ships with Chrome 33 which has, but let was only introduced Chrome 49 (41 with strict mode). So it's possible that SDK 22 won't be sufficient, depending on the end-users webview version but this is upgradeable and the latest version available for these devices is Chrome ~70.

Cordova-android@12 has a min SDK of 24 which AOSP simulators ships with Chrome 53. In all likeliness this is what most people will see.

Additionally I updated the README to mention these new requirements.

Testing

ran npm test

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary