No spellcheck

### Expected
I would expect when I make a spelling mistake, the app will help me auto-correct it (or at least show a red dotted line underneath the wrong word). This was working in the previous version of the app - 1.2.11.

### Observed
Nothing happens when I made a spelling mistake on the notes, even if I didn't capitalize the first character of the first word of the line.

### Reproduced

**Note:** The issue was originally reported in 3424081-zen for the Windows app but I'm able to replicate this on https://app.simplenote.com.

1. Log in to Simplenote app at https://app.simplenote.com/
2. Create a new note
3. Type a wrong word, e.g. contry
4. See that the app does nothing with the wrong word.

I would expect the word to be automatically corrected as `Country`, capitalized and spelling corrected.

### Where did you see the bug

- System Make: Apple
- System Model: iMac 27-inch
- OS: macOS
- OS version: Catalina 10.15.6
- Browser (if applicable): Google Chrome
- Browser version (if applicable): Version 86.0.4240.80 (Official Build) (x86_64)
- Simplenote app version: https://app.simplenote.com

#### Information reported in 3424081-zen

OS: Windows 10
Simplenote app version: 2.0.0

Reproduce the issue in the Simplenote web app at https://app.simplenote.com using the listed Chrome/macOS setup, and compare behavior with version 1.2.11 and the Windows 2.0.0 report. Investigate the notes editor and its spellcheck behavior; done means misspelled words are corrected or visibly marked, including the reported capitalization case.

Written by the indexing model from the issue text.