Update pyo3 to 0.8.

[sebpuetz]

Prerequisite for fixing #51

[sebpuetz]

I'm confused by the CI failures:

• TryFrom is stable since 1.34
• NonZeroI*are stable since 1.34

rustc version is 1.34, yet CI fails and I can't build locally either with the same toolchain.

[sebpuetz]

pyo3 requires nightly-2019-07-19-x86_64-unknown-linux-gnu on 0.8

[danieldk]

Looks good, but do we need all the updates in Cargo.lock? Or are they enforced by the pyo3 update? Seems like a lot of updates.

[danieldk]

Looks good, but do we need all the updates in Cargo.lock? Or are they enforced by the pyo3 update? Seems like a lot of updates.

Seems like there are more errors (CI fail).

[sebpuetz]

Looks good, but do we need all the updates in Cargo.lock? Or are they enforced by the pyo3 update? Seems like a lot of updates.

Looks like the rust plugin for CLion was doing its thing again. nevermind, just running pyo3-pack build --release changes a lot in Cargo.lock

Seems like there are more errors (CI fail).

I forgot to change the default toolchain, I had only updated the required rust version for travis-ci.

[danieldk]

Sorry for the slow ack. I was fighting my own Rust battles ;).