travis: pin meson to an older version so it works with Python 3.4 The CI image only has Python 3.4. It's a bit of a hassle to change this, so let's pin meson to the version before they bumped their requirement instead. I suppose it's not that bad in that it will guarantee compatibility with older meson over time. Signed-off-by: Ran Benita <ran234@gmail.com>