Update the README.md badges (#546)

`filter` in the Maven Central badge is a workaround for shields.io
always choosing the latest version (even if the version *prefix* is given).
See https://shields.io/badges/maven-central-version

Author: dkhalanskyjb

README.md

@@ -3,8 +3,8 @@
 [![Kotlin Alpha](https://kotl.in/badges/alpha.svg)](https://kotlinlang.org/docs/components-stability.html)
 [![JetBrains official project](https://jb.gg/badges/official.svg)](https://confluence.jetbrains.com/display/ALL/JetBrains+on+GitHub)
 [![GitHub license](https://img.shields.io/badge/license-Apache%20License%202.0-blue.svg?style=flat)](http://www.apache.org/licenses/LICENSE-2.0)
-[![Maven Central](https://img.shields.io/maven-central/v/org.jetbrains.kotlinx/kotlinx-datetime.svg?label=Maven%20Central)](https://search.maven.org/search?q=g:org.jetbrains.kotlinx%20AND%20a:kotlinx-datetime)
-[![Kotlin](https://img.shields.io/badge/kotlin-1.9.21-blue.svg?logo=kotlin)](http://kotlinlang.org)
+[![Maven Central](https://img.shields.io/maven-central/v/org.jetbrains.kotlinx/kotlinx-datetime?filter=0.7.0)](https://search.maven.org/search?q=g:org.jetbrains.kotlinx%20AND%20a:kotlinx-datetime)
+[![Kotlin](https://img.shields.io/badge/kotlin-2.1.20-blue.svg?logo=kotlin)](http://kotlinlang.org)
 [![KDoc link](https://img.shields.io/badge/API_reference-KDoc-blue)](https://kotlinlang.org/api/kotlinx-datetime/)
 [![Slack channel](https://img.shields.io/badge/chat-slack-blue.svg?logo=slack)](https://kotlinlang.slack.com/messages/kotlinx-datetime/)
 [![TeamCity build](https://img.shields.io/teamcity/build/s/KotlinTools_KotlinxDatetime_Build_All.svg?server=http%3A%2F%2Fteamcity.jetbrains.com)](https://teamcity.jetbrains.com/viewType.html?buildTypeId=KotlinTools_KotlinxDatetime_Build_All&guest=1)