fix formatting of fisher table

Lines up table borders output by the `fisher` tool, changing something like this
```
# Contingency Table
#_________________________________________
#        | not in -b    | in -b        |
# not in -a | 3137160615   | 100          |
#      in -a | 503          | 46           |
#_________________________________________
# p-values for fisher's exact test
left	right	two-tail	ratio
1	4.9743e-274	4.9743e-274	2868973.922
```
to this:
```
# Contingency Table
#__________________________________________
#            | not in -b    | in -b        |
#  not in -a | 3137160615   | 100          |
#      in -a | 503          | 46           |
#__________________________________________
# p-values for fisher's exact test
left	right	two-tail	ratio
1	4.9743e-274	4.9743e-274	2868973.922
```