Text style not applied

## Issue or Feature
I want to use SanFrancisco. I need Black and regular styles, but for some reason the style is not applied :(

## Steps to Reproduce
```js
registerFont(__dirname + "/fonts/regular.ttf", {family: "SF"});
registerFont(__dirname + "/fonts/black.ttf", {family: "SF", weight: "bold"});

const canvas = createCanvas(512, 512);
const ctx = canvas.getContext('2d');
ctx.fillStyle = '#ffffff';
ctx.fillRect(0, 0, 512, 512);

ctx.fillStyle = '#000000';
ctx.font = '125px SF';
ctx.fillText("First text", 0, 100);

ctx.font = 'bold 85px SF';
ctx.fillText("Second text", 0, 175);
```

## Your Environment
* Version of node-canvas - 2.6.1
* Environment node 12.18.4 on Windows 10