[Java]: Fix generated output formatting for indentation.

Author: mjpt777

main/java/uk/co/real_logic/sbe/generation/java/JavaGenerator.java

@@ -303,7 +303,8 @@ private void generateGroupClassHeader(
  ));
 
  sb.append(String.format(
- indent + " @Override\n public %s next()\n" +
+ indent + " @Override\n" +
+ indent + " public %s next()\n" +
  indent + " {\n" +
  indent + " if (index + 1 >= count)\n" +
  indent + " {\n" +