It's a Google Chrome Plugin. When you are using the WhatsApp Web, it makes capitalize the first letter of your sentences.
- Download this repo and extract
- Open Google Chrome
- Open the following URL chrome://extensions/
- Enable Developer Mode
- Click LOAD UNPACKED button and select the downloaded directory
- Open web.whatsapp.com in new tab
- Start Plugin
Note Stopping plugin doesn't work perfectly. Refresh the page after stop plugin.