Fix failing Travis build

[ErwinJanssen]

The Travis build of projects generated with this cookiecutter fail out of the box. The Travis build for the project itself is also failing. This pull request attempts to resolve this by:

• Updating the test setup of the project to match the setup of the generated project. The generated project seems to have a more modern approach, and keeping this uniform will improve maintainability.
• Update all dependencies to the most recent versions.
• Remove support for Python 2.6 (no longer supported by the Python core team) and Python 3.3 (not supported by Pytest)

Additionally, support for Python 3.6 was added, since this is the most recent version.

[hugovk]

👍

Remove support for Python 2.6 (no longer supported by the Python core team) and Python 3.3 (not supported by Pytest)

Yep, both Python 2.6 and 3.3 are no longer supported by the Python core team nor Pytest.

---

Here's the pip installs for cookiecutter from PyPI for last month, showing virtually nothing for 2.6 and 3.3:

python_version	percent	download_count
3.6	73.4%	77,025
2.7	24.3%	25,548
3.5	1.7%	1,759
3.4	0.5%	498
3.7	0.1%	76
3.3	0.0%	15
2.6	0.0%	8

Source: pypinfo --start-date -47 --end-date -17 --percent --pip --markdown cookiecutter pyversion

---

You could also update this to (3, 4) in test_bake_project.py:

    elif sys.version_info >= (3, 3):

(Then when 3.4 is ditched, the whole elif block can be removed.)