[Checkins] [zopefoundation/DocumentTemplate] d67cbe: No longer test on Python 2.6 on Travis.

[Maurits van Rees]

  Branch: refs/heads/plonehotfix2020-213
  Home:   https://github.com/zopefoundation/DocumentTemplate
  Commit: d67cbe854d7b4384c0695df3bbfb2dd9b1021548
      https://github.com/zopefoundation/DocumentTemplate/commit/d67cbe854d7b4384c0695df3bbfb2dd9b1021548
  Author: Maurits van Rees <maurits at vanrees.org>
  Date:   2020-01-31 (Fri, 31 Jan 2020)

  Changed paths:
    M .travis.yml

  Log Message:
  -----------
  No longer test on Python 2.6 on Travis.

This partially reverts fd562eabfa722c2c5f13185851604b1662b2e811 from 2018 which tried to fix Python 2.6.
Meanwhile 2.6 has become too hard.

See error on https://travis-ci.org/zopefoundation/DocumentTemplate/jobs/644398589

```
Downloading archive: https://storage.googleapis.com/travis-ci-language-archives/python/binaries/ubuntu/16.04/x86_64/python-2.6.tar.bz2
$ curl -sSf --retry 5 -o python-2.6.tar.bz2 ${archive_url}
curl: (22) The requested URL returned error: 404 Not Found
Unable to download 2.6 archive. The archive may not exist. Please consider a different version.
```