Update .travis.yml with wordpress 4.4, 4.3. Remove Wordpress 3.9 and 4.0

[benlk]

Changes

• Adds 4.4 and 4.3 to .travis.yml
• Removes the outdated 3.9 and 4.0
• Updates 4.1 and 4.2 to their latest bugfix versions.

This PR does not fix any tests. it only updates .travis.yml.

Why

Because #1020, and there might be tests failing as a result of changes in versions of WordPress.

[benlk]

• an error

1) PostTemplatesTestFunctions::test_insert_image_no_thumb
Indirect modification of overloaded property PostTemplatesTestFunctions::$ids has no effect
/tmp/wordpress/src/wp-content/themes/Largo/tests/inc/test-post-templates.php:77
/tmp/wordpress/src/wp-content/themes/Largo/tests/inc/test-post-templates.php:20

[benlk]

There are some tests here that are only failing under PHP 5.5, and some only under PHP 5.3.29, and some that only fail under WordPress 4.4.2 (current stable).

PHP 5.3 is end-of-life (1 year, 7 months ago), but we keep it around because the deploy-tools virtual machines use it (and use a version of Ubuntu 2 years old, without backports), and specifically use PHP 5.3.10. Without special work, the vagrant boxes will never receive PHP 5.3.29.

We don't need to keep PHP 5.3 support.

WP Engine uses PHP 5.5: http://phpinfo.wpengine.com/

They're our primary target.

Upgrading the virtualboxen to Ubuntu 14.04 from their current 12.04 will let us keep the LTS release, but bring PHP 5.5. 16.04 isn't out yet.

[aschweigert]

do we know what tests are failing?

[benlk]

• array to string conversion inside a related content function that gets the post before and after a given post: https://github.com/INN/Largo/blob/master/tests/inc/test-related-content.php#L441 (one errored test in PHP 5.5)
• this line in the update functions' run of the Custom LESS updater: https://github.com/INN/Largo/blob/1020-update-travis-latest-wordpress/inc/update.php#L510 (Non-static method Largo::is_less_enabled() should not be called statically) (causes two errored tests in PHP 5.5)
• Something changed in WordPress' taxonomy code in 4.4.x that makes the prominence term description updater fail in PHP 5.3.29 and 5.5.x: https://github.com/INN/Largo/blob/1020-update-travis-latest-wordpress/tests/inc/test-update.php#L333

Two update functions, one related content.