Font ligatures don't work v3

• I am on the latest Hyper.app version
• I have searched the issues of this repo and believe that this is not a duplicate

• OS version and name: 10.14.4 macOS Mojave
• Hyper.app version: 3.0.0
• Link of a Gist with the contents of your .hyper.js:
• Relevant information from devtools (CMD+ALT+I on macOS, CTRL+SHIFT+I elsewhere):
• The issue is reproducible in vanilla Hyper.app: Is Vanilla or with the hyper-font-ligatures add-on.

Issue

I'm using Fira Code font and the ligatures don't work. I found this issue https://github.com/zeit/hyper/issues/914 and tried installing the hyper-font-ligatures add-on or adding this css

termCSS: `
  x-screen x-row {
    font-variant-ligatures: initial;
  }
`,

but none of these seem to work.

Start by reproducing the Fira Code ligature failure in vanilla Hyper.app on macOS, then inspect the terminal rendering through DevTools. Compare the result with the hyper-font-ligatures add-on and the provided termCSS setting; done means ligatures render correctly without relying on an add-on.