fillStyle and strokeStyle fail when using fractional values on rgba

## Issue or Feature
Whenever you try to set a color style with fractional components like 'rgba(120.1, 120.2, 120.3, 1)', it fails to parse and defaults to a black color.

## Steps to Reproduce
```js
var Canvas = require('canvas');
var canvas = Canvas.createCanvas(200, 200);
var ctx = canvas.getContext('2d');
ctx.fillStyle = 'rgba(240.2,0,0,1)';
ctx.fillRect(20, 20, 40, 40);
```

Shows a black rectangle instead of a red one.

## Your Environment
node-canvas 2.7.0
Node is v12.16.1 on OS X Catalina 10.15.7