Add Django 1.11 to the test matrix

[jwalgran]

The updates to .travis.yml were made by running the command as directed in the comment.

I corrected a failing pylint check by removing an extraneous else from the module.

[bittner]

Thanks for this PR! I'll add a few comments.

[jwalgran]

After switching to the Travis trusty distribution, the 2.6 builds started failing.

ERROR:   flake8-py26: InterpreterNotFound: python2.6

Do you want to drop 2.6 from the build matrix?

[jwalgran]

The Travis docs lead me to believe that testing 2.6 through 3.6 should be possible

https://docs.travis-ci.com/user/languages/python/#Choosing-Python-versions-to-test-against

Trying out adding multiple versions to the python: key in .travis.yml.

[bittner]

Do you want to drop 2.6 from the build matrix?

If this is the only way to make builds with Python 3.5 and 3.6 pass, yes. It would be nice to keep it though.

The code base of this package is so simple that it still can run in super-outdated projects (namely the ones still running on Python 2.6). :smile:

[bittner]

The Travis docs lead me to believe that testing 2.6 through 3.6 should be possible

The challenge is the combination of the Python and Django versions. If you find a way, cool! If not, don't worry too much, and let's drop 2.6.

[jwalgran]

Specifying 2 versions

python:
  - 2.6
  - 3.6

resulted in Travis running the full matrix twice, so that is not the solution.

https://travis-ci.org/bittner/django-apptemplates/builds/250841808

[jwalgran]

Adding this before_install section to apt get the missing interpreters did the trick

before_install:
  - sudo add-apt-repository -y ppa:fkrull/deadsnakes
  - sudo apt-get -qq update
  - sudo apt-get -y install python2.6 python3.2

[bittner]

Thanks a million for your efforts, @jwalgran!