[Breaking change] default shadow blur value should be 0 (and not 1px)
![2018-06-25 12 56 49](https://user-images.githubusercontent.com/16788797/41820826-ac16d85e-7812-11e8-9ca0-b37185b51f68.png)

The default value of `blur` in `addInnerShadow` is `1`. 
Therefore, there is a problem that blur is applied.

two solutions.

The first is to add `blur: 0` in code of `one-side border.`
```javascript
if (borderTopWidthFloat !== 0) {
    style.addInnerShadow({color: borderTopColor, offsetY: borderTopWidthFloat, blur: 0});
}
```

Or, if blur's default has no reason. We can change it to 0.
```javascript
addInnerShadow({color = '#000', blur = 0, offsetX = 0, offsetY = 0, spread = 0}) {
...
```

What do you think about this?