fix bug that prevented overriding isGrammarFile()

src/main/java/org/jastadd/relast/compiler/RelAstProcessor.java

@@ -25,7 +25,7 @@ public abstract class RelAstProcessor extends AbstractCompiler {
     super(name, jastAddCompliant);
   }
 
-  protected static boolean isGrammarFile(String fileName) {
+  protected boolean isGrammarFile(String fileName) {
     String extension = fileName.subSequence(fileName.lastIndexOf('.'), fileName.length()).toString();
     return extension.equals(".relast") || extension.equals(".ast");
   }

src/main/java/org/jastadd/relast/compiler/RelastSourceToSourceCompiler.java

@@ -22,7 +22,8 @@ public class RelastSourceToSourceCompiler extends RelAstProcessor {
     }
   }
 
-  protected static boolean isGrammarFile(String fileName) {
+  @Override
+  protected boolean isGrammarFile(String fileName) {
     String extension = fileName.subSequence(fileName.lastIndexOf("."), fileName.length()).toString();
     return extension.equals(".relast") || extension.equals(".ast");
   }