Duplication of First letter in Korean

### Description

Typing in korean, the second letter gets along with first letter Duplicate 
### Steps to reproduce

1. Start typing in korean
2. If we type [ㅈㄷ] on UI we are able to see [ㅈㅈㄷ]
3. Once you refresh the page it is again happening!!!


**Link to an example:**  [JS Bin](https://jsbin.com/zowoqasoru/edit?html,output)

### Versions

- medium-editor:5.23.3
- browser:
- OS:
