Update shadow plugin to 7.1.2

Author: eygraber

build.gradle

@@ -1,13 +1,13 @@
 buildscript {
     repositories {
-        jcenter()
         mavenCentral()
+        gradlePluginPortal()
     }
 
     dependencies {
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion"
         classpath "org.jetbrains.kotlin:kotlin-serialization:$kotlinVersion"
-        classpath 'com.github.jengelman.gradle.plugins:shadow:5.0.0'
+        classpath 'gradle.plugin.com.github.johnrengelman:shadow:7.1.2'
         classpath "io.codearte.gradle.nexus:gradle-nexus-staging-plugin:0.21.2"
     }
 }
@@ -26,7 +26,6 @@ nexusStaging {
 allprojects {
     repositories {
         mavenCentral()
-        jcenter()
         maven {
             url = "https://kotlin.bintray.com/kotlinx/"
         }

danger-kotlin-kts/build.gradle

@@ -1,9 +1,9 @@
 buildscript {
     repositories {
-        jcenter()
+        gradlePluginPortal()
     }
     dependencies {
-        classpath 'com.github.jengelman.gradle.plugins:shadow:5.0.0'
+        classpath 'gradle.plugin.com.github.johnrengelman:shadow:7.1.2'
     }
 }