Upgrade to Java 11

Author: dondonz

build.gradle

@@ -31,14 +31,14 @@ version = releaseVersion ? releaseVersion : getDevelopmentVersion()
 println "Building version = " + version
 group = 'com.graphql-java'
 
-if (JavaVersion.current() != JavaVersion.VERSION_1_8) {
-    def msg = String.format("This build must be run with java 1.8 - you are running %s - gradle finds the JDK via JAVA_HOME=%s",
+if (JavaVersion.current() != JavaVersion.VERSION_11) {
+    def msg = String.format("This build must be run with Java 11 - you are running %s - gradle finds the JDK via JAVA_HOME=%s",
             JavaVersion.current(), System.getenv("JAVA_HOME"))
     throw new GradleException(msg)
 }
 
-sourceCompatibility = 1.8
-targetCompatibility = 1.8
+sourceCompatibility = JavaVersion.VERSION_11.toString()
+targetCompatibility = JavaVersion.VERSION_11.toString()
 
 repositories {
     mavenCentral()