Upgrade gradle, kotlin and README

[codecov[bot]]

Codecov Report

Base: 78.99% // Head: 78.88% // Decreases project coverage by -0.11% :warning:

Coverage data is based on head (e6c6d72) compared to base (f4937b3). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #175 +/- ## ============================================ - Coverage 78.99% 78.88% -0.12% Complexity 635 635 ============================================ Files 86 86 Lines 1757 1757 Branches 144 144 ============================================ - Hits 1388 1386 -2 - Misses 282 284 +2 Partials 87 87 ``` | [Impacted Files](https://codecov.io/gh/Smarteon/loxone-java/pull/175?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smarteon) | Coverage Δ | | |---|---|---| | [.../main/java/cz/smarteon/loxone/LoxoneWebSocket.java](https://codecov.io/gh/Smarteon/loxone-java/pull/175/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smarteon#diff-c3JjL21haW4vamF2YS9jei9zbWFydGVvbi9sb3hvbmUvTG94b25lV2ViU29ja2V0LmphdmE=) | `66.37% <0.00%> (-0.89%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smarteon). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smarteon)

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