Update kotlin version

Author: jakobkmar

buildSrc/build.gradle.kts

@@ -7,6 +7,6 @@ repositories {
 }
 
 dependencies {
-    implementation(kotlin("gradle-plugin", "1.4.21"))
+    implementation(kotlin("gradle-plugin", "1.4.30"))
     implementation("com.jfrog.bintray.gradle", "gradle-bintray-plugin", "1.8.5")
 }

simplekotlinmail-core/build.gradle.kts

@@ -11,7 +11,7 @@ plugins {
     `common-build-script`
     `java-version-script`
 
-    kotlin("plugin.serialization") version "1.4.21"
+    kotlin("plugin.serialization") version "1.4.30"
 
 }