Incorrect documentation for `check_point_order_equals_group_order`

In the documentation for `check_point_order_equals_group_order`,
https://github.com/ZenGo-X/curv/blob/44537a746292be65961e9c38191319c17a3d2977/src/elliptic/curves/traits.rs#L185

should presumably read

```    
/// P ≠ 0 ∧ qP = 0
```

The implementation appears to be correct, so just a simple doc fix should suffice.
