Add clippy config to travis CI.

[SingingTree]

This should have travis run clippy as well as fail if any warnings are
found (not just in clippy, but elsewhere too).

I think this should work, but given the matrix of configs it's possible something breaks, so suggest we keep an eye on travis for a bit if we merge this.

[SingingTree]

Looks like something is already unhappy. I'll iterate some more on this and update the PR once I've clobbered the issues.

[SingingTree]

Looks like I need to fix:

• Some of the tests don't play nicely if you check before running the tests. I.e. if you cargo check or cargo clippy then run cargo test --all the tests fail. Not sure why yet, but it's a problem that isn't unique to these changes.
• There look to be some nightly clippy lints that I missed.

[SingingTree]

#187 looks to fix the nightly lint issue. Now to try and fix the issue of cargo check before cargo test breaking the tests.

[SingingTree]

#197 is the issue blocking this.

[baumanj]

Could you do a similar workaround to 6c13760 and move the clippy run after cargo test?

[SingingTree]

Could you do a similar workaround to 6c13760 and move the clippy run after cargo test?

Indeed, and it's probably what I should do since I haven't come up with a better solution. That, or doing an extra clean felt like hacks, but probably better than letting this PR rot. I'd been hacking on this in my spare time rather than as a mozilla task, so I'll look for some spare time to get this across the line.

[baumanj]

Can this be reexamined in light of #281 ?

[SingingTree]

Superseded by #282.