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>

.travis.yml

@@ -6,7 +6,7 @@ before_install:
     - sudo apt-get update -qq
     - sudo apt-get -y install xutils-dev doxygen libxcb-xkb-dev python3-pip valgrind
     - wget https://github.com/ninja-build/ninja/releases/download/v1.7.2/ninja-linux.zip && unzip ninja-linux.zip && sudo install ninja /usr/bin/
-    - sudo pip3 install meson
+    - sudo pip3 install meson==0.44.1
 
 compiler:
     - gcc