Bump bytecode version

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/compiler/Compiler.java

@@ -206,7 +206,7 @@
  * Compiler for bytecode interpreter.
  */
 public class Compiler implements SSTreeVisitor<Void> {
-    public static final int BYTECODE_VERSION = 27;
+    public static final int BYTECODE_VERSION = 28;
 
     private final ErrorCallback errorCallback;