I just updated to 3.1 to see if that corrects the issue. It does not.

Given the following sample table

| P | Q | P * Q |
| - | - | - |
| T | T | T |
| T | F | F |
| F | T | F |
| F | F | F |

Gollum renders it as one line, not as a table:

atom renders it like a table:

According to the GFM wiki, tables are supported.