Ensure Travis fails fast

[0xazure]

In reviewing #34, I noticed one of the build jobs failed the clippy step but continued on to the test and build steps anyways. This seems like needless work, and it might be more desirable to tighten up the builds feedback on PRs so the build fails immediately if one of the checks like clippy or rustfmt fails.

@seanprashad does Travis not fail-fast, or do we need to configure something else? We already have fast_finish enabled in our config:

supernova/.travis.yml

Line 35 in 66f5bc5

fast_finish: true

[biskit1]

is it related to the fact that we allow failures for rust: nightly so all the tests against the nightly channel will still resume?

[0xazure]

No, the allow_failures for nightly means that the nightly job in the build matrix can fail but the entire build won't fail and e.g. merging a pull request won't be blocked. See: Rows that are Allowed to Fail.

Also, the specific job I linked to there is for the stable release channel, so it isn't affected by allowing failures for nightly.