bincode 1.0.0-alpha6 changed SizeLimit to a trait

[ms705]

Unfortunately, cargo's semantic versioning gets confused by the -alpha suffix in current bincode versions (I think): even though tarpc's Cargo.toml specified version 1.0.0-alpha4, cargo will download the more recent 1.0.0-alpha6, which has breaking changes to the SizeLimit enum.

This change makes tarpc work with bincode 1.0.0-alpha6 and updates the dependency.

Fixes #133 for me.

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[tikue]

Thanks! Looks like there are Travis failures?

[ms705]

Those are due to cargo #3844, and hopefully fixed in the latest nightly!

[ms705]

(Also, I signed the CLA.)

[googlebot]

CLAs look good, thanks!

[tikue]

Thanks again!