Strict Java 8 feature check on build

Author: Querela

pom.xml

@@ -19,6 +19,7 @@
         <!-- plug-in settings -->
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
+        <maven.compiler.release>8</maven.compiler.release>
         <!-- versions and settings of common dependencies -->
         <antlr.version>4.13.2</antlr.version>
         <antlr4.visitor>true</antlr4.visitor>