Unicode characters mess up table alignment

[SidOfc]

This is related to #80 regarding the use of unicode characters in the input lines.

OS type:

• Unix
• Windows
• Other (macOS)

Vim:

• vim
• neovim
• Other ([SPECIFY])

Vim version:

v0.3.1

Reproduce steps:

Example:

1. Open a markdown file.
2. Paste the following example into the file:

   first,second
   😀 list item,😀 list item

3. Then, from Normal mode with the cursor on the first line, go into visual-block mode V and select the second line as well with j and convert to CSV with Leader+,.

Expected:

|     first      |     second     |
|:--------------:|:--------------:|
|  😀 list item  |  😀 list item  |

(even github shows a small deviation)

Actual:

|     first      |     second     |
|:--------------:|:--------------:|
| 😀 list item | 😀 list item |