switch to java 11, and use JastAdd plugin properly

.gitlab-ci.yml

@@ -29,7 +29,7 @@ cache:
     - .gradle/caches
 
 build:
-  image: openjdk:8
+  image: openjdk:11
   stage: build
   script:
     - ./gradlew --console=plain assemble
@@ -38,7 +38,7 @@ build:
       - "eraser-base/src/gen"
 
 test:
-  image: openjdk:8
+  image: openjdk:11
   tags:
     - docker
   stage: test

buildSrc/src/main/groovy/eraser.java-common-conventions.gradle

@@ -9,6 +9,12 @@ repositories {
   mavenCentral()
 }
 
+java {
+  toolchain {
+    languageVersion = JavaLanguageVersion.of(11)
+  }
+}
+
 dependencies {
   implementation group: 'org.apache.logging.log4j', name: 'log4j-api', version: "${log4j_version}"
   implementation group: 'org.apache.logging.log4j', name: 'log4j-core', version: "${log4j_version}"

buildSrc/src/main/groovy/eraser.java-jastadd-conventions.gradle

 plugins {
   id 'eraser.java-common-conventions'
   id 'java-library'
+  id 'jastadd'
 }
 
 dependencies {

settings.gradle

+pluginManagement {
+  plugins {
+    id 'org.jastadd' version '1.13.3'
+  }
+}
+
 rootProject.name = 'eraser'
 
 include ':eraser-base'