Travis CI: Add the long dead Python 2.6

[cclauss]

Checklist

• npm install && npm test passes
• tests are included
• documentation is changed or added
• commit message follows commit guidelines

Description of change

As discussed in #1912, we need to test software that we claim to support.

[rvagg]

remade the branch and cherry-picked the HEAD commit onto it so it's properly on v5.x now, will watch Travis to see what it says, regardless I don't think this is (a) needed or (b) requires us to document it, it's just not something we can change on v5.x because it's been baked in already.

[cclauss]

I rebased on v5.x at same time you did so who knows what we got. Let’s see what Travis says. If it fails then I believe our release notes should reflect that.

[cclauss]

Flake8 no longer supports Python 2.6 but even when flake8 is fully disabled, the Py26 run fails.

[rvagg]

it failed because it's running Node 0.10 on that image, I switched to 10 (nvm install 10), but then it failed because it didn't have semverRange, so I rebased onto rvagg/restore-python-2.6, but then it's failing because the compilers is too old on precise: https://travis-ci.com/nodejs/node-gyp/jobs/242023105, but that's a pretty good sign that it actually works, or at least it's not failing because of Python 2.6, it's making the build resources so getting cleanly through gyp. Would be interesting to figure out how to make this run. Can we do 2.6 on a newer image than precise?

[cclauss]

Try upgrading to trusty

[rvagg]

green with trusty 👍 will merge this into v5.x

[rvagg]

No, I won't add this, because it disables flake8 for everything, we'll need to differentiate before it can land. I've cleaned it up into a single commit on top of the current v5.x and force pushed it up.