make stable compile after syntex update

[TeXitoi]

Right now, a checkout of rs-es or a cargo update on a project using rs-es 0.3.1 does not compile on stable (and potentially on others channels).

At the same time, remove 2 warnings.

[coveralls]

Coverage remained the same at 50.246% when pulling 8732593 on TeXitoi:make_stable_compile into 2467300 on benashford:master.

[benashford]

Cool, thanks for this!

It looks like the change of serde_codegen from 0.7.1 to 0.7.2 pulls in a newer quasi and that introduces the build problems. I might lock that dependency to prevent this happening in later versions.

In the meantime I'll merge this and push a new release.

Thanks again.

[benashford]

Published as 0.3.2

[TeXitoi]

Great! Thanks for the reactivity.