HTML5Validator and Travis

[dontcallmedom]

Running HTML5Validator requires operating with Oracle JDK8, but the current Travis set up used here comes with JDK7.

The JDK is customizable in a language: java environment, but we need the python one otherwise the python part of the script fails.

Options include:

• switching to the beta Trusty environment
• looking at whether the JDK can be switched by another magic command in the current precise environment (jdk-switcher?)