Publish Grace plugins to the Gradle Plugin Portal

Closes gh-844

Author: rainboyan

grace-gradle-plugin/build.gradle

@@ -1,14 +1,10 @@
 buildscript {
     repositories {
-        maven { url "https://plugins.gradle.org/m2/" }
-        maven { url 'https://repo.gradle.org/gradle/libs-releases' }
+        gradlePluginPortal()
+    }
+    dependencies {
+        classpath("com.gradle.plugin-publish:com.gradle.plugin-publish.gradle.plugin:1.3.0")
     }
-}
-
-repositories {
-    mavenCentral()
-    maven { url "https://repo.grails.org/grails/core" }
-    maven { url 'https://repo.gradle.org/gradle/libs-releases' }
 }
 
 ext.isSnapshot = version.endsWith("-SNAPSHOT")
@@ -17,6 +13,7 @@ ext."signing.keyId" = System.getenv("SIGNING_KEY") ?: project.hasProperty("signi
 ext."signing.password" = System.getenv("SIGNING_PASSPHRASE") ?: project.hasProperty("signing.password") ? project.getProperty('signing.password') : null
 ext."signing.secretKeyRingFile" = project.hasProperty("signing.secretKeyRingFile") ? project.getProperty('signing.secretKeyRingFile') : null
 
+apply plugin: 'com.gradle.plugin-publish'
 apply plugin: 'java-gradle-plugin'
 apply plugin: 'maven-publish'