Scryer-prolog: compilation fails on master still

[srenatus]

Despite having the NegAssign issue resolved, it seems travis still isn't happy.

👉 Errors start here: https://travis-ci.com/github/mthom/scryer-prolog/jobs/318812557#L672 and it's mostly type mismatches, like

   --> src/prolog/arithmetic.rs:434:53
    |
434 |                 Ok(Number::from(Integer::from(n1) + &*n2))
    |                                                     ^^^^
    |                                                     |
    |                                                     expected struct `prolog::rug::Integer`, found `&prolog::rug::Integer`
    |                                                     help: consider removing the borrow: `*n2`
error[E0308]: mismatched types

[srenatus]

To reproduce this locally, it's cargo build --no-default-features --features num.

[mthom]

I just made a pull request to num-rug-adapter to fix this. I will update Scryer to use it once it's accepted and published to cargo. That should put the build errors to rest.

[mthom]

The Travis build now passes.

[srenatus]

Thank you 🚀