Adapte travis to new file architectures.

- kiwix-build is installable, so let's install it in travisCI
- Declare the dependency to meson in the setup.py
- As kiwixbuild is installed, we don't need to change the `sys.path`

setup.py

@@ -34,6 +34,9 @@ setup(
     ],
     packages=find_packages(),
     include_package_data=True,
+    install_requires=[
+        'meson==0.43.0'
+    ],
     entry_points={
         'console_scripts': [
             'kiwix-build = kiwixbuild:main'