Need to add a write barrier for ranges; fix #4042

Ranges are almost immutable but `initialize` and `initialize_copy`
modify the receiver so that we need to add a write barrier.

src/range.c

@@ -120,6 +120,7 @@ range_init(mrb_state *mrb, mrb_value range, mrb_value beg, mrb_value end, mrb_bo
   }
   r->edges->beg = beg;
   r->edges->end = end;
+  mrb_write_barrier(mrb, (struct RBasic*)r);
 }
 /*
  *  call-seq: