Not enough hyphens/dash between the table header and rows

[jjnilton]

It seems the markdown doesn't output enough dashes/hyphens between the table header and its rows, which make the markdown source slightly less readable.

Org input:

* The first heading

| word    | number |
|---------+--------|
| one     |      1 |
| ten     |     10 |
| hundred |    100 |

Current behavior:

# The first heading

| word    | number |
|------- |------ |
| one     | 1      |
| ten     | 10     |
| hundred | 100    |

Expected:

# The first heading

| word    | number |
|---------|--------|
| one     | 1      |
| ten     | 10     |
| hundred | 100    |