Bump multiplatform from 1.6.20-RC2 to 1.6.20 (#103)

Bumps multiplatform from 1.6.20-RC2 to 1.6.20.

---
updated-dependencies:
- dependency-name: multiplatform
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

build.gradle.kts

@@ -6,7 +6,7 @@ import org.jetbrains.dokka.gradle.*
  */
 
 plugins {
-    kotlin("multiplatform") version "1.6.20-RC2" apply false
+    kotlin("multiplatform") version "1.6.20" apply false
     kotlin("plugin.serialization") version "1.6.20" apply false
     id("org.jetbrains.kotlinx.binary-compatibility-validator") version "0.8.0"
     `maven-publish`