Use javac release-flag to compile for correct classpath (String#isBlank is used => minimum JDK is 11)

Author: matthiasblaesing

pom.xml

@@ -80,9 +80,8 @@
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>8</maven.compiler.source>
-        <maven.compiler.target>8</maven.compiler.target>
         <version.antlr>4.13.1</version.antlr>
+        <maven.compiler.release>11</maven.compiler.release>
     </properties>
 
     <dependencies>