Fix multiple styles with margin

I found an issue when trying to apply multiple styles with margin to a node. This pull fixes the issue.

**Configuration:**

```javascript
styles: {
    header: {
        color: "gray"
    },
    indent: {
        margin: [20, 0, 0, 0]
    }
}
```

**Node:**

```javascript
{ text: "Test 1", style: ["header", "indent"] }
```