Array#fill not compliant with MRI 

**Expected Behavior**
```
2.6.4 :001 > [:foo].fill(nil,2,0)
 => [:foo, nil]
```
```
3.1.3 :001 > [:foo].fill(nil,2,0)
 => [:foo, nil]
```

**Actual Behavior**
```
jruby-9.3.9.0 :001 > [:foo].fill(nil,2,0)
 => [:foo]
```
```
jruby-9.4.1.0 :006 > [:foo].fill(nil,2,0)
 => [:foo]
```