writing over initial placeholder text without deleting it and error when submitting said text

**Describe the bug**
hi i was using this fork and bumped into this problem i would appreciate a fix or some guide in what am i doing wrong, thanks alot, the bug is this:

when i write over the initial placeholder text it doesnt deletes it and writes "on top" of the text and error when submitting said text because the text submitted is empty
see screenshot

**To Reproduce**
Steps to reproduce the behavior:
1. Go to a form with a textarea with easymde on chrome or firefox on android
2. Touch the textarea and write sometext
3. Submit form
4. See error while writing the text or while submitting the form with a restriction to not allow empty text

**Expected behavior**
The placeholder text should be deleted, and the submitted text should not be empty server side

**Screenshots**
[easymde screenshot of the error](https://i.imgur.com/sVoJRtP.png)

** Version information **
- OS: Android 10
- Browser: Chrome (80.0.3987.87)
- EasyMDE version: 2.9.0

**Additional context**
the form doesnt allow empty text

Start by reproducing the issue with an EasyMDE textarea on Android Chrome or Firefox, checking both the visible placeholder behavior and the value submitted by the form. Done means typing replaces the initial text and the server receives the entered content rather than an empty value.

Written by the indexing model from the issue text.