Build failed on rustc nightly-2017-09-16

[messense]

Caused by rust-lang/rust#43017

Depends on spin-rs: zesterer/spin-rs#42

Ref #5

[fafhrd91]

we can vendor spin-rs

[fafhrd91]

@messense let's use your fork of spin-rs, until author accept PR.

[messense]

Added a daily cron build job on Travis CI so that we can detect nightly breakage faster.

[messense]

spin-rs released the fixed version on crates.io.

[fafhrd91]

thanks