Fix Travis CI

[nfriedly]

No rush on this. I thought you might appreciate it, though, and it'll certainly make me feel a little more confident about my PRs.

This includes a few changes to test against current versions of PHP and avoid incompatibilities:

• Moved PHP 5.3 builds to Ubuntu Precise, because Travis CI doesn't support 5.3 on the default Trusty distro.
  • HHVM is only avaliable on Trusty, so just moving everything to Precise wasn't an option.
• Include PHP 7.0, 7.1, and 7.2
• Only test WP 3.8 on PHP < 7.0
  • This is because WP 3.8 depends on mysql_connect(), which was removed in PHP 7.0
• Allow failures on PHP nightly
  • It's currently failing, but as far as I can tell, it's a bug in PHP, not your code.

With these changes, you now have a green build - see https://travis-ci.org/nfriedly/DsgnWrks-Instagram-Importer/builds/431689310

I structured things so that current-gen stuff is the "default" and legacy stuff is added to the matrix one-at-a-time. It's a little verbose, but it has a benefit of allowing you to add future versions of PHP and WordPress without having to remember to exclude the legacy stuff.

I'm targeting this PR at future but it should be easy enough to cherry-pick onto master if you'd like, especially if you squash-and-merge.

[jtsternberg]

Beautiful. We should discuss co-maintainership. Are you open to the idea?

[nfriedly]

Yea, I'm happy to help out. It's been quite a while since I've done any php, but it seems like WordPress is pretty adamant about supporting older versions, so I'm not missing much in this context.