Update failure, serde, structopt

[sanxiyn]

Conservatively update dependencies so that we use syn and quote 1.0 and only single version of them.

This time I didn't forget to run cargo test!

[mattias-p]

What difference does this make? Smaller binary size?
Is there some property here that ought to be maintained over time? If so, do you know of a good way to detect regressions?

[sanxiyn]

There should be no visible differences to users. These are procedural macros, so not smaller binary size.

I guess it does save compile time, since syn and quote are fairly large and now they are not compiled twice. cargo tree -d (for duplicate) can print dependencies with multiple versions.

[mattias-p]

Sorry for letting you wait :( My life got in the way.
Cargo tree is pretty neat! But what a mess it reveals.
Well, I see no harm in these changes.