[travis-ci] Download, install and use Maven 3.1.1

There is no reason for red build while waiting for Travis CI team to
make Maven 3.1.1 available out of the box.

Signed-off-by: Mykola Nikishov <mn@mn.com.ua>
Merge pull request #237 from manandbytes/travis-mvn311

[travis-ci] Download, install and use Maven 3.1.1