Remove reference to specific gender ratios

[ntlk]

1. When referring to people it’s preferable to speak about men and women. “Males” and “females” can equally refer to animals, so it’s more respectable to use human-specific language.
2. The previous phrasing wasn’t particularly inclusive for people outside of the gender binary.
3. It’s unclear where the 2:1 ratio comes from. Unless there is some clear evidence for it I think the first sentence of the rule is helpful enough.

[ntlk]

Thanks @olleolleolle!