Upgrades in next Linux VM update

This a WIP pull request to track the documentation of version upgrades coming with next Linux VM update. Please don't merge yet...

**Done:**
* ... (coming soon ;)

**WIP:**
* Maven 3.1.0, confirmed, but doc change will be added to this branch after merging #358)
* Gradle 1.8, confirmed, but doc change will be added after merging #358)
* Clang 3.3, update not confirmed yet (see travis-ci/travis-cookbooks#212)