Don't bother with lts-3 and lts-5 builds
Don't bother with lts-3 and lts-5 builds

These will fail; eg:

- https://travis-ci.org/wincent/docvim/jobs/139231414
- https://travis-ci.org/wincent/docvim/jobs/139231416

Because a recent version of hlint (not available in the old lts snapshots) is
required in order to do CPP conditionals properly; see:

- https://github.com/ndmitchell/hlint/issues/239

wincent/docvim