Updated My5Heap class and resolve #4

Can declare a local variable `int lastChildren = (hole*5 + 5 > size-1) ? size-1 : hole*5 + 5` to replace
```java
if(hole*5+5>size-1){
  for(int j=child;j<size-1;j++) {
    //codes
  }
  //codes
} else {
  for(int i=child;i<child+4;i++) {
    //codes
  }
  //codes
}
```

with

```java
for(int i=child;i<=lastChildren;i++) {
  //codes
}
//codes
```

because the codes inside are pretty much the same.