tables missing

### Is this a hackmd.io issue?

- [x] Yes, the bug happens on https://hackmd.io
- [ ] No. If it's a self-hosted CodiMD instance, please fire up the issue in the repo of CodiMD: https://github.com/hackmdio/codimd

### Read our Official tutorial

It's on https://hackmd.io/c/tutorials/

或是中文版 https://hackmd.io/c/tutorials-tw/

### What's the problem
No tables symbol in toolbar as suggested in doc https://hackmd.io/c/tutorials/%2F%40docs%2Fhow-to-create-table-en
#### Current behaviour

> Screenshot (optional)

Provide steps to reproduce:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

If possible, create a note with reproducible content and share the link with us.

e.g. note link: https://hackmd.io/features

#### Expected behaviour

(description of expected behaviour)

#### Environment

I use HackMD on:

**Desktop**
- OS: [eg. macOS]
- Browser: [e.g. chrome, safari, firefox, opera]
- Browser Version: [71]

**Mobile**

- Device: [e.g. iPhone XS]
- OS: [e.g. iOS 12.1]
- Browser: [e.g. chrome, safari]
- Version: [e.g. 23]

#### Additional context

Add any other context about the problem here.