Resolve "Make grammar(s) more concise"

Closes #40 (closed)

ragconnect.base/build.gradle

@@ -24,6 +24,9 @@ repositories {
     mavenCentral()
     jcenter()
 }
+tasks.compileJava {
+    options.release.set(11)
+}
 
 dependencies {
     implementation project(':relast-preprocessor')
@@ -33,6 +36,12 @@ dependencies {
     api group: 'net.sf.beaver', name: 'beaver-rt', version: '0.9.11'
 }
 
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(11))
+    }
+}
+
 def versionFile = 'src/main/resources/ragConnectVersion.properties'
 def props = new Properties()