Resolve "Upgrade to Java 11"

Closes #45 (closed)

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}"